How to allow a space into a wildcard? - r

Question

Let's say I have this sentence :
text<-("I want to find both the greatest cake of the world but also some very great cakes but I want to find this last part : isn't it")
When I write this (kwicis a quantedafunction) :
kwic(text,phrase("great* cake*"))
I get
[text1, 7:8] want to find both the | greatest cake | of the world but also
[text1, 16:17] world but also some very | great cakes | but I want to find
However, when I do
kwic(text,phrase("great*cake*"))
I get a kwicobject with 0 row, i.e. nothing
I would like to know what does the *replace exactly and, more important, how to "allow" a space to be taken into account in the wildcard ?

Answer 1

To answer what the * matches, you need to understand the "glob" valuetype, which you can read about using ?valuetype and also here. In short, * matches any number of any characters including none. Note that this is very different from its use in a regular expression, which means "match none or more of the preceding character".
The pattern argument in kwic() matches one pattern per token, after tokenizing the text. Even wrapped in the phrase() function, it still only considers sequences of matches to tokens. So you cannot match the whitespace (which defines the boundaries between tokens) unless you actually include these inside the token's value itself.
How could you do that? Like this:
toksbi <- tokens(text, ngrams = 2, concatenator = " ")
# tokens from 1 document.
# text1 :
# [1] "I want" "want to" "to find" "find both" "both the"
# [6] "the greatest" "greatest cake" "cake of" "of the" "the world"
# [11] "world but" "but also" "also some" "some very" "very great"
# [16] "great cakes" "cakes but" "but I" "I want" "want to"
# [21] "to find" "find this" "this last" "last part" "part :"
# [26] ": isn't" "isn't it"
kwic(toksbi, "great*cake*", window = 2)
# [text1, 7] both the the greatest | greatest cake | cake of of the
# [text1, 16] some very very great | great cakes | cakes but but I
But your original usage of kwic(text, phrase("great* cake*")) is the recommended approach.