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lift_curve() constructs the full lift curve and returns a
tibble. See gain_curve() for a closely related concept.
lift_curve(data, ...)# S3 method for data.frame
lift_curve(data, truth, ..., na_rm = TRUE)
autoplot.lift_df(object, ...)
A data.frame containing the truth and estimate
columns.
A set of unquoted column names or one or more
dplyr selector functions to choose which variables contain the
class probabilities. If truth is binary, only 1 column should be selected.
Otherwise, there should be as many columns as factor levels of truth.
The column identifier for the true class results
(that is a factor). This should be an unquoted column name although
this argument is passed by expression and supports
quasiquotation (you can unquote column
names). For _vec() functions, a factor vector.
A logical value indicating whether NA
values should be stripped before the computation proceeds.
The lift_df data frame returned from lift_curve().
A tibble with class lift_df or lift_grouped_df having
columns:
.n - The index of the current sample.
.n_events - The index of the current unique sample. Values with repeated
estimate values are given identical indices in this column.
.percent_tested - The cumulative percentage of values tested.
.lift - First calculate the cumulative percentage of true results relative to the
total number of true results. Then divide that by .percent_tested.
The motivation behind cumulative gain and lift charts is as a visual method to determine the effectiveness of a model when compared to the results one might expect without a model. As an example, without a model, if you were to advertise to a random 10% of your customer base, then you might expect to capture 10% of the of the total number of positive responses had you advertised to your entire customer base. Given a model that predicts which customers are more likely to respond, the hope is that you can more accurately target 10% of your customer base and capture >10% of the total number of positive responses.
The calculation to construct lift curves is as follows:
truth and estimate are placed in descending order by the estimate
values (estimate here is a single column supplied in ...).
The cumulative number of samples with true results relative to the entire number of true results are found.
The cumulative % found is divided by the cumulative % tested to construct the lift value. This ratio represents the factor of improvement over an uninformed model. Values >1 represent a valuable model. This is the y-axis of the lift chart.
If a multiclass truth column is provided, a one-vs-all
approach will be taken to calculate multiple curves, one per level.
In this case, there will be an additional column, .level,
identifying the "one" column in the one-vs-all calculation.
There is no common convention on which factor level should
automatically be considered the "event" or "positive" result.
In yardstick, the default is to use the first level. To
change this, a global option called yardstick.event_first is
set to TRUE when the package is loaded. This can be changed
to FALSE if the last level of the factor is considered the
level of interest by running: options(yardstick.event_first = FALSE).
For multiclass extensions involving one-vs-all
comparisons (such as macro averaging), this option is ignored and
the "one" level is always the relevant result.
There is a ggplot2::autoplot()
method for quickly visualizing the curve. This works for
binary and multiclass output, and also works with grouped data (i.e. from
resamples). See the examples.
Other curve metrics: gain_curve,
pr_curve, roc_curve
# NOT RUN {
# ---------------------------------------------------------------------------
# Two class example
# `truth` is a 2 level factor. The first level is `"Class1"`, which is the
# "event of interest" by default in yardstick. See the Relevant Level
# section above.
data(two_class_example)
# Binary metrics using class probabilities take a factor `truth` column,
# and a single class probability column containing the probabilities of
# the event of interest. Here, since `"Class1"` is the first level of
# `"truth"`, it is the event of interest and we pass in probabilities for it.
lift_curve(two_class_example, truth, Class1)
# ---------------------------------------------------------------------------
# `autoplot()`
library(ggplot2)
library(dplyr)
# Use autoplot to visualize
autoplot(lift_curve(two_class_example, truth, Class1))
# Multiclass one-vs-all approach
# One curve per level
hpc_cv %>%
filter(Resample == "Fold01") %>%
lift_curve(obs, VF:L) %>%
autoplot()
# Same as above, but will all of the resamples
hpc_cv %>%
group_by(Resample) %>%
lift_curve(obs, VF:L) %>%
autoplot()
# }
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