CODEWITHSUNDEEP
r
Tyler Rinker
Tyler Rinker

Reputation: 109844

matching a numeric list of vectors to a character list of vectors

I have a list of character strings (vectors) and I have a list of numeric vectors that I want to use to find the words from the first. I have it arranged as a data table below to help you visualize:

                                  words neg2
1 i, do, not, like, when, she, is, mean 2, 8
2               i, think, its, not, bad 1, 4

I want to extract the 2nd and 8th word from the character string for row one and then the 1st and fourth words from the character string for row 2 as shown in the MATCH column below:

                                 words neg2    MATCH
1 i, do, not, like, when, she, is, mean 2, 8 do, mean
2               i, think, its, not, bad 1, 4   i, not

Code to reproduce the 2 lists:

neg2<-list(c(2, 8), c(1, 4))
x$words <-list(c("i", "do", "not", "like", "when", "she", "is", "mean"), 
    c("i", "think", "its", "not", "bad"))

I know this is easy I'm just not seeing it. I've tried using match(), with lapply() and various other combinations but am coming up short.

I'd appreciate the most efficient way to achieve this.

Upvotes: 1

Views: 253

Answers (2)

Rguy
Rguy

Reputation: 1652

words <- list(c("i", "do", "not", "like", "when", "she", "is", "mean"), 
    c("i", "think", "its", "not", "bad"))
neg2<-list(c(2, 8), c(1, 4))
words[[1]][neg2[[1]]]
words[[2]][neg2[[2]]]

Or, for arbitrarily long lists of words and indexes:

words1 <- list()
for(i in 1:length(words)) {
    words1[[i]] <- words[[i]][neg2[[i]]]
}

Looks like you just need to understand how to index lists in R. See http://cran.r-project.org/doc/manuals/R-lang.html#Indexing

Upvotes: 0

Tyler Rinker
Tyler Rinker

Reputation: 109844

I just realized mapply is the answer:

SEL<-function(x, y)x[y]
mapply(SEL, x$words, neg2, SIMPLIFY = FALSE)

Upvotes: 3

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