dfm-class: Virtual class "dfm" for a document-feature matrix

Description

The dfm class of object is a type of Matrix-class object with additional slots, described below. quanteda uses two subclasses of the dfm class, depending on whether the object can be represented by a sparse matrix, in which case it is a dfmSparse class object, or if dense, then a dfmDense object. See Details.

Usage

# S4 method for dfmDense
t(x)
# S4 method for dfmSparse
t(x)
# S4 method for dfmSparse
colSums(x, na.rm = FALSE, dims = 1L, ...)
# S4 method for dfmSparse
rowSums(x, na.rm = FALSE, dims = 1L, ...)
# S4 method for dfmSparse
colMeans(x, na.rm = FALSE, dims = 1L, ...)
# S4 method for dfmSparse
rowMeans(x, na.rm = FALSE, dims = 1L, ...)
# S4 method for dfmSparse,numeric
+(e1, e2)
# S4 method for numeric,dfmSparse
+(e1, e2)
# S4 method for dfmDense,numeric
+(e1, e2)
# S4 method for numeric,dfmDense
+(e1, e2)
# S4 method for dfm,index,index,missing
[(x, i, j, ..., drop = FALSE)
# S4 method for dfm,index,index,logical
[(x, i, j, ..., drop = FALSE)
# S4 method for dfm,missing,missing,missing
[(x, i, j, ..., drop = FALSE)
# S4 method for dfm,missing,missing,logical
[(x, i, j, ..., drop = FALSE)
# S4 method for dfm,index,missing,missing
[(x, i, j, ..., drop = FALSE)
# S4 method for dfm,index,missing,logical
[(x, i, j, ..., drop = FALSE)
# S4 method for dfm,missing,index,missing
[(x, i, j, ..., drop = FALSE)
# S4 method for dfm,missing,index,logical
[(x, i, j, ..., drop = FALSE)

Arguments

the dfm object

na.rm

if TRUE, omit missing values (including NaN) from the calculations

dims

ignored

...

additional arguments not used here

first quantity in "+" operation for dfm

second quantity in "+" operation for dfm

index for documents

index for features

drop

always set to FALSE

Slots

settings: settings that govern corpus handling and subsequent downstream operations, including the settings used to clean and tokenize the texts, and to create the dfm. See settings.

weighting

the feature weighting applied to the dfm. Default is "frequency", indicating that the values in the cells of the dfm are simple feature counts. To change this, use the weight method.

smooth

a smoothing parameter, defaults to zero. Can be changed using either the smooth or the weight methods.

Dimnames

These are inherited from Matrix-class but are named docs and features respectively.

Details

The dfm class is a virtual class that will contain one of two subclasses for containing the cell counts of document-feature matrixes: dfmSparse or dfmDense.

The dfmSparse class is a sparse matrix version of dfm-class, inheriting dgCMatrix-class from the Matrix package. It is the default object type created when feature counts are the object of interest, as typical text-based feature counts tend contain many zeroes. As long as subsequent transformations of the dfm preserve cells with zero counts, the dfm should remain sparse.

When the Matrix package implements sparse integer matrixes, we will switch the default object class to this object type, as integers are 4 bytes each (compared to the current numeric double type requiring 8 bytes per cell.)

The dfmDense class is a sparse matrix version of dfm-class, inheriting dgeMatrix-class from the Matrix package. dfm objects that are converted through weighting or other transformations into cells without zeroes will be automatically converted to the dfmDense class. This will necessarily be a much larger sized object than one of dfmSparse class, because each cell is recorded as a numeric (double) type requiring 8 bytes of storage.

Examples

Run this code

# NOT RUN {
# dfm subsetting
x <- dfm(tokens(c("this contains lots of stopwords",
                  "no if, and, or but about it: lots",
                  "and a third document is it"),
                remove_punct = TRUE))
x[1:2, ]
x[1:2, 1:5]

# fcm subsetting
y <- fcm(tokens(c("this contains lots of stopwords",
                  "no if, and, or but about it: lots"),
                remove_punct = TRUE))
y[1:3, ]
y[4:5, 1:5]
# }