dfm_match: Match the feature set of a dfm to given feature names
In koheiw/quanteda.core: Quantitative Analysis of Textual Data

Description Usage Arguments Details Value Note See Also Examples

Match the feature set of a dfm to a specified vector of feature names. For existing features in x for which there is an exact match for an element of features, these will be included. Any features in x not features will be discarded, and any feature names specified in features but not found in x will be added with all zero counts.

1	dfm_match(x, features)

`x`	a dfm
`features`	character; the feature names to be matched in the output dfm

Selecting on another dfm's featnames() is useful when you have trained a model on one dfm, and need to project this onto a test set whose features must be identical.

A dfm whose features are identical to those specified in features.

Unlike dfm_select(), this function will add feature names not already present in x. It also provides only fixed, case-sensitive matches. For more flexible feature selection, see dfm_select().

dfm_select()

# matching a dfm to a feature vector
dfm_match(dfm(""), letters[1:5])
dfm_match(data_dfm_lbgexample, c("A", "B", "Z"))
dfm_match(data_dfm_lbgexample, c("B", "newfeat1", "A", "newfeat2"))

# matching one dfm to another
txt <- c("This is text one", "The second text", "This is text three")
(dfmat1 <- dfm(txt[1:2]))
(dfmat2 <- dfm(txt[2:3]))
(dfmat3 <- dfm_match(dfmat1, featnames(dfmat2)))
setequal(featnames(dfmat2), featnames(dfmat3))