# sentimentr v2.7.1

0

0th

Percentile

## Calculate Text Polarity Sentiment

Calculate text polarity sentiment at the sentence level and optionally aggregate by rows or grouping variable(s).

# sentimentr

sentimentr is designed to quickly calculate text polarity sentiment at the sentence level and optionally aggregate by rows or grouping variable(s).

sentimentr is a response to my own needs with sentiment detection that were not addressed by the current R tools. My own polarity function in the qdap package is slower on larger data sets. It is a dictionary lookup approach that tries to incorporate weighting for valence shifters (negation and amplifiers/deamplifiers). Matthew Jockers created the syuzhet package that utilizes dictionary lookups for the Bing, NRC, and Afinn methods as well as a custom dictionary. He also utilizes a wrapper for the Stanford coreNLP which uses much more sophisticated analysis. Jocker's dictionary methods are fast but are more prone to error in the case of valence shifters. Jocker's addressed these critiques explaining that the method is good with regard to analyzing general sentiment in a piece of literature. He points to the accuracy of the Stanford detection as well. In my own work I need better accuracy than a simple dictionary lookup; something that considers valence shifters yet optimizes speed which the Stanford's parser does not. This leads to a trade off of speed vs. accuracy. Simply, sentimentr attempts to balance accuracy and speed.

# Why sentimentr

So what does sentimentr do that other packages don't and why does it matter?

sentimentr attempts to take into account valence shifters (i.e., negators, amplifiers (intensifiers), de-amplifiers (downtoners), and adversative conjunctions) while maintaining speed. Simply put, sentimentr is an augmented dictionary lookup. The next questions address why it matters.

So what are these valence shifters?

A negator flips the sign of a polarized word (e.g., "I do not like it."). See lexicon::hash_valence_shifters[y==1] for examples. An amplifier (intensifier) increases the impact of a polarized word (e.g., "I really like it."). See lexicon::hash_valence_shifters[y==2] for examples. A de-amplifier (downtoner) reduces the impact of a polarized word (e.g., "I hardly like it."). See lexicon::hash_valence_shifters[y==3] for examples. An adversative conjunction overrules the previous clause containing a polarized word (e.g., "I like it but it's not worth it."). See lexicon::hash_valence_shifters[y==4] for examples.

Do valence shifters really matter?

Well valence shifters affect the polarized words. In the case of negators and adversative conjunctions the entire sentiment of the clause may be reversed or overruled. So if valence shifters occur fairly frequently a simple dictionary lookup may not be modeling the sentiment appropriately. You may be wondering how frequently these valence shifters co-occur with polarized words, potentially changing, or even reversing and overruling the clause's sentiment. The table below shows the rate of sentence level co-occurrence of valence shifters with polarized words across a few types of texts.

Cannon reviews 21% 23% 8% 12%
2012 presidential debate 23% 18% 1% 11%
Trump speeches 12% 14% 3% 10%
Trump tweets 19% 18% 4% 4%
Dylan songs 4% 10% 0% 4%
Austen books 21% 18% 6% 11%
Hamlet 26% 17% 2% 16%

Indeed negators appear ~20% of the time a polarized word appears in a sentence. Conversely, adversative conjunctions appear with polarized words ~10% of the time. Not accounting for the valence shifters could significantly impact the modeling of the text sentiment.

The script to replicate the frequency analysis, shown in the table above, can be accessed via:

val_shift_freq <- system.file("the_case_for_sentimentr/valence_shifter_cooccurrence_rate.R", package = "sentimentr")
file.copy(val_shift_freq, getwd())


# Functions

There are two main functions (top 2 in table below) in sentimentr with several helper functions summarized in the table below:

Function Description
sentiment Sentiment at the sentence level
sentiment_by Aggregated sentiment by group(s)
profanity Profanity at the sentence level
profanity_by Aggregated profanity by group(s)
emotion Emotion at the sentence level
emotion_by Aggregated emotion by group(s)
uncombine Extract sentence level sentiment from sentiment_by
get_sentences Regex based string to sentence parser (or get sentences from sentiment/sentiment_by)
replace_emoji repalcement
replace_emoticon Replace emoticons with word equivalent
replace_grade Replace grades (e.g., "A+") with word equivalent
replace_internet_slang replacment
replace_rating Replace ratings (e.g., "10 out of 10", "3 stars") with word equivalent
as_key Coerce a data.frame lexicon to a polarity hash key
is_key Check if an object is a hash key
update_key Add/remove terms to/from a hash key
highlight Highlight positive/negative sentences as an HTML document
general_rescale Generalized rescaling function to rescale sentiment scoring
sentiment_attribute Extract the sentiment based attributes from a text
validate_sentiment Validate sentiment score sign against known results

# The Equation

The equation below describes the augmented dictionary method of sentimentr that may give better results than a simple lookup dictionary approach that does not consider valence shifters. The equation used by the algorithm to assign value to polarity of each sentence fist utilizes a sentiment dictionary (e.g., Jockers, (2017)) to tag polarized words. Each paragraph (pi = {s1, s2, ..., sn}) composed of sentences, is broken into element sentences (si, j = {w1, w2, ..., wn}) where w are the words within sentences. Each sentence (sj) is broken into a an ordered bag of words. Punctuation is removed with the exception of pause punctuations (commas, colons, semicolons) which are considered a word within the sentence. I will denote pause words as c**w (comma words) for convenience. We can represent these words as an i,j,k notation as wi, j, k. For example w3, 2, 5 would be the fifth word of the second sentence of the third paragraph. While I use the term paragraph this merely represent a complete turn of talk. For example it may be a cell level response in a questionnaire composed of sentences.

The words in each sentence (wi, j, k) are searched and compared to a dictionary of polarized words (e.g., a combined and augmented version of Jocker's (2017) [originally exported by the syuzhet package] & Rinker's augmented Hu & Liu (2004) dictionaries in the lexicon package). Positive (wi, j, k+) and negative (wi, j, k) words are tagged with a +1 and −1 respectively (or other positive/negative weighting if the user provides the sentiment dictionary). I will denote polarized words as p**w for convenience. These will form a polar cluster (ci, j, l) which is a subset of the a sentence (ci, j, l ⊆ si, j).

The polarized context cluster (ci, j, l) of words is pulled from around the polarized word (p**w) and defaults to 4 words before and two words after p**w to be considered as valence shifters. The cluster can be represented as (ci, j, l = {p**wi, j, k − n**b, ..., p**wi, j, k, ..., p**wi, j, k − n**a}), where n**b & n**a are the parameters n.before and n.after set by the user. The words in this polarized context cluster are tagged as neutral (wi, j, k0), negator (wi, j, kn), amplifier [intensifier] (wi, j, ka), or de-amplifier [downtoner] (wi, j, kd). Neutral words hold no value in the equation but do affect word count (n). Each polarized word is then weighted (w) based on the weights from the polarity_dt argument and then further weighted by the function and number of the valence shifters directly surrounding the positive or negative word (p**w). Pause (c**w) locations (punctuation that denotes a pause including commas, colons, and semicolons) are indexed and considered in calculating the upper and lower bounds in the polarized context cluster. This is because these marks indicate a change in thought and words prior are not necessarily connected with words after these punctuation marks. The lower bound of the polarized context cluster is constrained to max{p**wi, j, k − n**b, 1, max{c**wi, j, k < p**wi, j, k}} and the upper bound is constrained to min{p**wi, j, k + n**a, wi, j**n, min{c**wi, j, k > p**wi, j, k}} where wi, j**n is the number of words in the sentence.

The core value in the cluster, the polarized word is acted upon by valence shifters. Amplifiers increase the polarity by 1.8 (.8 is the default weight (z)). Amplifiers (wi, j, ka) become de-amplifiers if the context cluster contains an odd number of negators (wi, j, kn). De-amplifiers work to decrease the polarity. Negation (wi, j, kn) acts on amplifiers/de-amplifiers as discussed but also flip the sign of the polarized word. Negation is determined by raising −1 to the power of the number of negators (wi, j, kn) plus 2. Simply, this is a result of a belief that two negatives equal a positive, 3 negatives a negative, and so on.

The adversative conjunctions (i.e., 'but', 'however', and 'although') also weight the context cluster. An adversative conjunction before the polarized word (wadversativeconjunction, ..., wi, j, kp) up-weights the cluster by 1 + z2 * {|wadversativeconjunction|,...,wi, j, kp} (.85 is the default weight (z2) where |wadversativeconjunction| are the number of adversative conjunctions before the polarized word). An adversative conjunction after the polarized word down-weights the cluster by 1 + {wi, j, kp, ..., |wadversativeconjunction|* − 1}*z2. This corresponds to the belief that an adversative conjunction makes the next clause of greater values while lowering the value placed on the prior clause.

The researcher may provide a weight (z) to be utilized with amplifiers/de-amplifiers (default is .8; de-amplifier weight is constrained to −1 lower bound). Last, these weighted context clusters (ci, j, l) are summed (ci, j) and divided by the square root of the word count (√wi, j**n) yielding an unbounded polarity score (δi, j) for each sentence.

δi**j = c'i**j/√wijn

Where:

ci, j = ∑((1 + wamp + wdeamp)⋅wi, j, kp(−1)2 + wneg)

wamp = ∑(wneg ⋅ (z ⋅ wi, j, ka))

wdeamp = max(wdeamp, −1)

wdeamp = ∑(z(−wneg ⋅ wi, j, ka + wi, j, kd))

wb = 1 + z2 * wb

wb = ∑(|wadversativeconjunction|,...,wi, j, kp, wi, j, kp, ..., |wadversativeconjunction|* − 1)

wneg = (∑wi, j, kn ) mod 2

To get the mean of all sentences (si, j) within a paragraph/turn of talk (pi) simply take the average sentiment score pi, δi, j = 1/n ⋅ ∑ δi, j or use an available weighted average (the default average_weighted_mixed_sentiment which upweights the negative values in a vector while also downweighting the zeros in a vector or average_downweighted_zero which simply downweights the zero polarity scores).

# Installation

Download the zip ball or tar ball, decompress and run R CMD INSTALL on it, or use the pacman package to install the development version:

if (!require("pacman")) install.packages("pacman")


# Examples

if (!require("pacman")) install.packages("pacman")


## Preferred Workflow

Here is a basic sentiment demo. Notice that the first thing you should do is to split your text data into sentences (a process called sentence boundary disambiguation) via the get_sentences function. This can be handled within sentiment (i.e., you can pass a raw character vector) but it slows the function down and should be done one time rather than every time the function is called. Additionally, a warning will be thrown if a larger raw character vector is passed. The preferred workflow is to spit the text into sentences with get_sentences before any sentiment analysis is done.

mytext <- c(
'do you like it?  But I hate really bad dogs',
'I am the best friend.',
'Do you really like it?  I\'m not a fan'
)

mytext <- get_sentences(mytext)
sentiment(mytext)

##    element_id sentence_id word_count  sentiment
## 1:          1           1          4  0.2500000
## 2:          1           2          6 -1.8677359
## 3:          2           1          5  0.5813777
## 4:          3           1          5  0.4024922
## 5:          3           2          4  0.0000000


To aggregate by element (column cell or vector element) use sentiment_by with by = NULL.

mytext <- c(
'do you like it?  But I hate really bad dogs',
'I am the best friend.',
'Do you really like it?  I\'m not a fan'
)
mytext <- get_sentences(mytext)
sentiment_by(mytext)

##    element_id word_count       sd ave_sentiment
## 1:          1         10 1.497465    -0.8088680
## 2:          2          5       NA     0.5813777
## 3:          3          9 0.284605     0.2196345


To aggregate by grouping variables use sentiment_by using the by argument.

(out <- with(
presidential_debates_2012,
sentiment_by(
get_sentences(dialogue),
list(person, time)
)
))

##        person   time word_count        sd ave_sentiment
##  1:     OBAMA time 1       3599 0.2535006    0.12256892
##  2:     OBAMA time 2       7477 0.2509177    0.11217673
##  3:     OBAMA time 3       7243 0.2441394    0.07975688
##  4:    ROMNEY time 1       4085 0.2525596    0.10151917
##  5:    ROMNEY time 2       7536 0.2205169    0.08791018
##  6:    ROMNEY time 3       8303 0.2623534    0.09968544
##  7:   CROWLEY time 2       1672 0.2181662    0.19455290
##  8:    LEHRER time 1        765 0.2973360    0.15473364
##  9:  QUESTION time 2        583 0.1756778    0.03197751
## 10: SCHIEFFER time 3       1445 0.2345187    0.08843478


## Tidy Approach

Or if you prefer a more tidy approach:

library(magrittr)
library(dplyr)

presidential_debates_2012 %>%
dplyr::mutate(dialogue_split = get_sentences(dialogue)) %$% sentiment_by(dialogue_split, list(person, time)) ## person time word_count sd ave_sentiment ## 1: OBAMA time 1 3599 0.2535006 0.12256892 ## 2: OBAMA time 2 7477 0.2509177 0.11217673 ## 3: OBAMA time 3 7243 0.2441394 0.07975688 ## 4: ROMNEY time 1 4085 0.2525596 0.10151917 ## 5: ROMNEY time 2 7536 0.2205169 0.08791018 ## 6: ROMNEY time 3 8303 0.2623534 0.09968544 ## 7: CROWLEY time 2 1672 0.2181662 0.19455290 ## 8: LEHRER time 1 765 0.2973360 0.15473364 ## 9: QUESTION time 2 583 0.1756778 0.03197751 ## 10: SCHIEFFER time 3 1445 0.2345187 0.08843478  Note that you can skip the dplyr::mutate step by using get_sentences on a data.frame as seen below: presidential_debates_2012 %>% get_sentences() %$%
sentiment_by(dialogue, list(person, time))

##        person   time word_count        sd ave_sentiment
##  1:     OBAMA time 1       3599 0.2535006    0.12256892
##  2:     OBAMA time 2       7477 0.2509177    0.11217673
##  3:     OBAMA time 3       7243 0.2441394    0.07975688
##  4:    ROMNEY time 1       4085 0.2525596    0.10151917
##  5:    ROMNEY time 2       7536 0.2205169    0.08791018
##  6:    ROMNEY time 3       8303 0.2623534    0.09968544
##  7:   CROWLEY time 2       1672 0.2181662    0.19455290
##  8:    LEHRER time 1        765 0.2973360    0.15473364
##  9:  QUESTION time 2        583 0.1756778    0.03197751
## 10: SCHIEFFER time 3       1445 0.2345187    0.08843478


## Plotting

### Plotting at Aggregated Sentiment

plot(out)


### Plotting at the Sentence Level

The plot method for the class sentiment uses syuzhet's get_transformed_values combined with ggplot2 to make a reasonable, smoothed plot for the duration of the text based on percentage, allowing for comparison between plots of different texts. This plot gives the overall shape of the text's sentiment. The user can see syuzhet::get_transformed_values for more details.

plot(uncombine(out))


## Making and Updating Dictionaries

It is pretty straight forward to make or update a new dictionary (polarity or valence shifter). To create a key from scratch the user needs to create a 2 column data.frame, with words on the left and values on the right (see ?lexicon::hash_sentiment_jockers_rinker & ?lexicon::hash_valence_shifters for what the values mean). Note that the words need to be lower cased. Here I show an example data.frame ready for key conversion:

set.seed(10)
key <- data.frame(
words = sample(letters),
polarity = rnorm(26),
stringsAsFactors = FALSE
)


This is not yet a key. sentimentr provides the is_key function to test if a table is a key.

is_key(key)

## [1] FALSE


It still needs to be data.table-ified. The as_key function coerces a data.frame to a data.table with the left column named x and the right column named y. It also checks the key against another key to make sure there is not overlap using the compare argument. By default as_key checks against valence_shifters_table, assuming the user is creating a sentiment dictionary. If the user is creating a valence shifter key then a sentiment key needs to be passed to compare instead and set the argument sentiment = FALSE. Below I coerce key to a dictionary that sentimentr can use.

mykey <- as_key(key)


Now we can check that mykey is a usable dictionary:

is_key(mykey)

## [1] TRUE


The key is ready for use:

sentiment_by("I am a human.", polarity_dt = mykey)

##    element_id word_count sd ave_sentiment
## 1:          1          4 NA    -0.7594893


You can see the values of a key that correspond to a word using data.table syntax:

mykey[c("a", "b")][[2]]

## [1] -0.2537805 -0.1951504


Updating (adding or removing terms) a key is also useful. The update_key function allows the user to add or drop terms via the x (add a data.frame) and drop (drop a term) arguments. Below I drop the "a" and "h" terms (notice there are now 24 rows rather than 26):

mykey_dropped <- update_key(mykey, drop = c("a", "h"))
nrow(mykey_dropped)

## [1] 24

sentiment_by("I am a human.", polarity_dt = mykey_dropped)

##    element_id word_count sd ave_sentiment
## 1:          1          4 NA     -0.632599


Next I add the terms "dog" and "cat" as a data.frame with sentiment values:

mykey_added <- update_key(mykey, x = data.frame(x = c("dog", "cat"), y = c(1, -1)))

## Warning in as_key(x, comparison = comparison, sentiment = sentiment): Column 1 was a factor...
## Converting to character.

## [1] 28

sentiment("I am a human. The dog.  The cat", polarity_dt = mykey_added)

##    element_id sentence_id word_count  sentiment
## 1:          1           1          4 -0.7594893
## 2:          1           2          2  0.7071068
## 3:          1           3          2 -0.7071068


## Annie Swafford's Examples

Annie Swafford critiqued Jocker's approach to sentiment and gave the following examples of sentences (ase for Annie Swafford example). Here I test each of Jocker's 4 dictionary approaches (syuzhet, Bing, NRC, Afinn), his Stanford wrapper (note I use my own GitHub Stanford wrapper package based off of Jocker's approach as it works more reliably on my own Windows machine), the RSentiment package, the lookup based SentimentAnalysis package, the meanr package (written in C level code), and my own algorithm with default combined Jockers (2017) & Rinker's augmented Hu & Liu (2004) polarity lexicons as well as Hu & Liu (2004) and Baccianella, Esuli and Sebastiani's (2010) SentiWord lexicons available from the lexicon package.

if (!require("pacman")) install.packages("pacman")

ase <- c(
"I haven't been sad in a long time.",
"I am extremely happy today.",
"It's a good day.",
"But suddenly I'm only a little bit happy.",
"Then I'm not happy at all.",
"In fact, I am now the least happy person on the planet.",
"There is no happiness left in me.",
"Wait, it's returned!",
"I don't feel so bad after all!"
)

syuzhet <- setNames(as.data.frame(lapply(c("syuzhet", "bing", "afinn", "nrc"),
function(x) get_sentiment(ase, method=x))), c("jockers", "bing", "afinn", "nrc"))

SentimentAnalysis <- apply(analyzeSentiment(ase)[c('SentimentGI', 'SentimentLM', 'SentimentQDAP') ], 2, round, 2)
colnames(SentimentAnalysis) <- gsub('^Sentiment', "SA_", colnames(SentimentAnalysis))

left_just(data.frame(
stanford = sentiment_stanford(ase)[["sentiment"]],
sentimentr_jockers_rinker = round(sentiment(ase, question.weight = 0)[["sentiment"]], 2),
sentimentr_jockers = round(sentiment(ase, lexicon::hash_sentiment_jockers, question.weight = 0)[["sentiment"]], 2),
sentimentr_huliu = round(sentiment(ase, lexicon::hash_sentiment_huliu, question.weight = 0)[["sentiment"]], 2),
sentimentr_sentiword = round(sentiment(ase, lexicon::hash_sentiment_sentiword, question.weight = 0)[["sentiment"]], 2),
RSentiment = calculate_score(ase),
SentimentAnalysis,
meanr = score(ase)[['score']],
syuzhet,
sentences = ase,
stringsAsFactors = FALSE
), "sentences")

[1] "Processing sentence: i have not been sad in a long time"
[1] "Processing sentence: i am extremely happy today"
[1] "Processing sentence: its a good day"
[1] "Processing sentence: but suddenly im only a little bit happy"
[1] "Processing sentence: then im not happy at all"
[1] "Processing sentence: in fact i am now the least happy person on the planet"
[1] "Processing sentence: there is no happiness left in me"
[1] "Processing sentence: wait its returned"
[1] "Processing sentence: i do not feel so bad after all"

stanford sentimentr_jockers_rinker sentimentr_jockers sentimentr_huliu
1     -0.5                      0.18               0.18             0.35
2        1                       0.6                0.6              0.8
3      0.5                      0.38               0.38              0.5
4     -0.5                         0                  0                0
5     -0.5                     -0.31              -0.31            -0.41
6     -0.5                      0.04               0.04             0.06
7     -0.5                     -0.28              -0.28            -0.38
8        0                     -0.14              -0.14                0
9     -0.5                      0.28               0.28             0.38
sentimentr_sentiword RSentiment SA_GI SA_LM SA_QDAP meanr jockers bing
1                 0.18          1 -0.25     0   -0.25    -1    -0.5   -1
2                 0.65          1  0.33  0.33       0     1    0.75    1
3                 0.32          1   0.5   0.5     0.5     1    0.75    1
4                    0          0     0  0.25    0.25     1    0.75    1
5                -0.56         -1     1     1       1     1    0.75    1
6                 0.11          1  0.17  0.17    0.33     1    0.75    1
7                -0.05          1   0.5   0.5     0.5     1    0.75    1
8                -0.14         -1     0     0       0     0   -0.25    0
9                 0.24          0 -0.33 -0.33   -0.33    -1   -0.75   -1
afinn nrc sentences
1    -2   0 I haven't been sad in a long time.
2     3   1 I am extremely happy today.
3     3   1 It's a good day.
4     3   1 But suddenly I'm only a little bit happy.
5     3   1 Then I'm not happy at all.
6     3   1 In fact, I am now the least happy person on the planet.
7     2   1 There is no happiness left in me.
8     0  -1 Wait, it's returned!
9    -3  -1 I don't feel so bad after all!


Also of interest is the computational time used by each of these methods. To demonstrate this I increased Annie's examples by 100 replications and microbenchmark on a few iterations (Stanford takes so long I didn't extend to more). Note that if a text needs to be broken into sentence parts syuzhet has the get_sentences function that uses the openNLP package, this is a time expensive task. sentimentr uses a much faster regex based approach that is nearly as accurate in parsing sentences with a much lower computational time. We see that RSentiment and Stanford take the longest time while sentimentr and syuzhet are comparable depending upon lexicon used. meanr is lighting fast. SentimentAnalysis is a bit slower than other methods but is returning 3 scores from 3 different dictionaries. I do not test RSentiment because it causes an out of memory error.

ase_100 <- rep(ase, 100)

stanford <- function() {sentiment_stanford(ase_100)}

sentimentr_jockers_rinker <- function() sentiment(ase_100, lexicon::hash_sentiment_jockers_rinker)
sentimentr_jockers <- function() sentiment(ase_100, lexicon::hash_sentiment_jockers)
sentimentr_huliu <- function() sentiment(ase_100, lexicon::hash_sentiment_huliu)
sentimentr_sentiword <- function() sentiment(ase_100, lexicon::hash_sentiment_sentiword)

RSentiment <- function() calculate_score(ase_100)

SentimentAnalysis <- function() analyzeSentiment(ase_100)

meanr <- function() score(ase_100)

syuzhet_jockers <- function() get_sentiment(ase_100, method="syuzhet")
syuzhet_binn <- function() get_sentiment(ase_100, method="bing")
syuzhet_nrc <- function() get_sentiment(ase_100, method="nrc")
syuzhet_afinn <- function() get_sentiment(ase_100, method="afinn")

microbenchmark(
stanford(),
sentimentr_jockers_rinker(),
sentimentr_jockers(),
sentimentr_huliu(),
sentimentr_sentiword(),
#RSentiment(),
SentimentAnalysis(),
syuzhet_jockers(),
syuzhet_binn(),
syuzhet_nrc(),
syuzhet_afinn(),
meanr(),
times = 3
)

Unit: milliseconds
expr          min           lq         mean
stanford() 20225.158418 20609.912899 23748.607689
sentimentr_jockers_rinker()   283.271569   283.391307   285.273047
sentimentr_jockers()   224.436569   228.487136   235.022980
sentimentr_huliu()   255.438460   260.156352   261.994973
sentimentr_sentiword()  1048.496476  1060.058681  1064.804513
SentimentAnalysis()  4267.380620  4335.857740  4369.068442
syuzhet_jockers()   342.764273   346.408800   349.115379
syuzhet_binn()   258.453721   267.449255   271.441450
syuzhet_nrc()   642.814135   648.150176   653.361347
syuzhet_afinn()   118.191289   120.576642   122.294740
meanr()     1.172578     1.317333     1.795786
median          uq          max neval
20994.667381 25510.33232 30025.997269     3
283.511045   286.27379   289.036528     3
232.537703   240.31619   248.094669     3
264.874245   265.27323   265.672214     3
1071.620886  1072.95853  1074.296176     3
4404.334860  4419.91235  4435.489845     3
350.053327   352.29093   354.528537     3
276.444790   277.93532   279.425840     3
653.486217   658.63495   663.783689     3
122.961995   124.34647   125.730937     3
1.462088     2.10739     2.752692     3


## Comparing sentimentr, syuzhet, meanr, and Stanford

The accuracy of an algorithm weighs heavily into the decision as to what approach to take in sentiment detection. I have selected algorithms/packages that stand out as fast and/or accurate to perform benchmarking on actual data. The syuzhet package provides multiple dictionaries with a general algorithm to compute sentiment scores. Likewise, sentimentr uses a general algorithm but uses the lexicon package's dictionaries. syuzhet provides 4 dictionaries while sentimentr uses lexicon's 9 dictionaries and can be extended easily other dictionaries including the 4 dictionaries from the syuzhet package. meanr is a very fast algorithm. The follow visualization provides the accuracy of these approaches in comparison to Stanford's Java based implementation of sentiment detection. The visualization is generated from testing on three reviews data sets from Kotzias, Denil, De Freitas, & Smyth (2015). These authors utilized the three 1000 element data sets from:

• amazon.com
• imdb.com
• yelp.com

The data sets are hand scored as either positive or negative. The testing here uses Mean Directional Accuracy (MDA)) and merely matches the sign of the algorithm to the human coded output to determine accuracy rates.

The bar graph on the left shows the accuracy rates for the various sentiment set-ups in the three review contexts. The rank plot on the right shows how the rankings for the methods varied across the three review contexts.

The take away here seems that, unsurprisingly, Stanford's algorithm consistently outscores sentimentr, syuzhet, and meanr. The sentimentr approach loaded with the Jockers' custom syuzhet dictionary is a top pick for speed and accuracy. In addition to Jockers' custom dictionary the bing dictionary also performs well within both the syuzhet and sentimentr algorithms. Generally, the sentimentr algorithm out performs syuzhet when their dictionaries are comparable.

It is important to point out that this is a small sample data set that covers a narrow range of uses for sentiment detection. Jockers' syuzhet was designed to be applied across book chunks and it is, to some extent, unfair to test it out of this context. Still this initial analysis provides a guide that may be of use for selecting the sentiment detection set up most applicable to the reader's needs.

The reader may access the R script used to generate this visual via:

testing <- system.file("sentiment_testing/sentiment_testing.R", package = "sentimentr")
file.copy(testing, getwd())


In the figure below we compare raw table counts as a heat map, plotting the predicted values from the various algorithms on the x axis versus the human scored values on the y axis.

Across all three contexts, notice that the Stanford coreNLP algorithm is better at:

• Detecting negative sentiment as negative
• Discrimination (i.e., reducing neutral assignments)

The Jockers, Bing, Hu & Lu, and Afinn dictionaries all do well with regard to not assigning negative scores to positive statements, but perform less well in the reverse, often assigning positive scores to negative statements, though Jockers' dictionary outperforms the others. We can now see that the reason for the NRC's poorer performance in accuracy rate above is its inability to discriminate. The Sentiword dictionary does well at discriminating (like Stanford's coreNLP) but lacks accuracy. We can deduce two things from this observation:

1. Larger dictionaries discriminate better (Sentiword [n = 20,093] vs. Hu & Lu [n = 6,874])
2. The Sentiword dictionary may have words with reversed polarities

A reworking of the Sentiword dictionary may yield better results for a dictionary lookup approach to sentiment detection, potentially, improving on discrimination and accuracy.

The reader may access the R script used to generate this visual via:

testing2 <- system.file("sentiment_testing/raw_results.R", package = "sentimentr")
file.copy(testing2, getwd())


## Text Highlighting

The user may wish to see the output from sentiment_by line by line with positive/negative sentences highlighted. The highlight function wraps a sentiment_by output to produces a highlighted HTML file (positive = green; negative = pink). Here we look at three random reviews from Hu and Liu's (2004) Cannon G3 Camera Amazon product reviews.

library(magrittr)
library(dplyr)
set.seed(2)

hu_liu_cannon_reviews %>%
filter(review_id %in% sample(unique(review_id), 3)) %>%
mutate(review = get_sentences(text)) %\$%
sentiment_by(review, review_id) %>%
highlight()


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