CODEWITHSUNDEEP
rstringlistsapplystringr
Damian
Damian

Reputation: 526

Extract and paste multiple elements from a list of lists generated by strsplit

I am trying to extract and paste together elements of a list of lists generated using strsplit. For example:

cat<-c("X0831_d8_f1_2s_wt_8_ROI_009", "X0831_d8_f1_2s_wt_8_ROI_008", 
"X0831_d8_f1_2s_wt_8_ROI_007", "X0831_d8_f1_2s_wt_8_ROI_006", 
"X0831_d8_f1_2s_wt_8_ROI_005", "X0831_d8_f1_2s_wt_8_ROI_004", 
"X0831_d8_f1_2s_wt_8_ROI_003", "X0831_d8_f1_2s_wt_8_ROI_002", 
"X0831_d8_f1_2s_wt_8_ROI_001", "X0831_d8_f1_10s_wt_8_ROI_019", 
"X0831_d8_f1_10s_wt_8_ROI_018")

I can generate the desired character vector using ldply:

mouse<-ldply(strsplit(cat, "_"))
paste(mouse$V4,mouse$V8,sep="_")

but was looking for a more elegant method of doing it. Perhaps using sapply or something similar?

I can generate a character vector containing one element:

sapply(strsplit(cat, "_"), "[[",4 )

but can't figure out a way to extract both elements (and paste them together).

Upvotes: 1

Views: 2037

Answers (1)

jeremycg
jeremycg

Reputation: 24945

Your example in plyr is pretty nice already, but here's how to do it in sapply, using an anonymous function:

sapply(strsplit(cat, "_"), function(x){paste(x[[4]], x[[8]], sep="_")})

The apply family, and several other functions can use anonymous functions, where you define them in the call. In this case, we have a function that takes each member of the list (as x), and then pastes the x[[4]] and x[[8]] together.

Upvotes: 3

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