R 匹配短语中的整个单词

Question

I have a character vector

var1 <- c("pine tree", "forest", "fruits", "water")

and a list

var2 <- list(c("tree", "house", "star"),  c("house", "tree", "pine tree", "tree pine", "dense forest"), c("apple", "orange", "grapes"))

I want to match words in var1 with words in var2, and extract the maximum matching element in var2. For example,

[[1]]
[1] "tree"  "house" "star" 

has 1 match with var1

[[2]]
[1] "house"        "tree"         "pine tree"    "tree pine"    "dense forest"

has 4 matches with var1

[[3]]
[1] "apple"  "orange" "grapes"

has 0 match with var1

And the desired output is the following:

[[2]]
[1] "house"        "tree"         "pine tree"    "tree pine"    "dense forest"

I tried

sapply(var1, grep,  var2, ignore.case=T, value=T)

without getting the output desired.

How to solve it? A code snippet would be appreciated. Thanks.

Answer 1

We create a pattern string ('pat') for the grepl , by first splitting the 'var1' by space '\\\\s+' . The output will be a list. We use sapply to loop over the list, use paste with collapse= '|' , and then collapse the whole vector to a single string with another paste . The | acts as OR while using as pattern for grepl in v1 . The sum vector ('v1') will be used for subsetting the list 'var2' based on the condition described in the question.

 pat <- paste(sapply(strsplit(var1, '\\s+'), function(x)
     paste(unique(c(x, paste(x, collapse=' '))), collapse='|')),
     collapse='|')
 v1 <- sapply(var2, function(x) sum(grepl(pat, x)))
 v1
 #[1] 1 4 0
 var2[which.max(v1)]
 #[[1]]
 #[1] "house"        "tree"         "pine tree"    "tree pine"    "dense forest"