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Counting and correlating pairs of words with the widyr package

30-03-2019  0 Comment(s)

Tokenizing by n-gram is a useful way to explore pairs of adjacent words. However, we may also be interested in words that tend to co-occur within particular documents or particular chapters, even if they don’t occur next to each other.

Tidy data is a useful structure for comparing between variables or grouping by rows, but it can be challenging to compare between rows: for example, to count the number of times that two words appear within the same document, or to see how correlated they are. Most operations for finding pairwise counts or correlations need to turn the data into a wide matrix first.

The philosophy behind the widyr package, which can perform operations such as counting and correlating on pairs of values in a tidy dataset. The widyr package first ‘casts’ a tidy dataset into a wide matrix, performs an operation such as a correlation on it, then re-tidies the result.

We’ll examine some of the ways tidy text can be turned into a wide matrix in Chapter 5, but in this case it isn’t necessary. The widyr package makes operations such as computing counts and correlations easy, by simplifying the pattern of “widen data, perform an operation, then re-tidy data” (Figure 4.7). We’ll focus on a set of functions that make pairwise comparisons between groups of observations (for example, between documents, or sections of text).

 

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