How to select values of a list based on another list in R?-CodePudding

I have a list that has values

c("December 2022","November 2022")

I have another list that has

c("December 2022/File1.xlsx","December 2022/File2.xlsx","October 2022/File1.xlsx",
"October 2022/File2.xlsx","November 2022/File1.xlsx","November 2022/File2.xlsx")

I want to pull from second list only the ones that start with the values in the first list. My final list should include

c("December 2022/File1.xlsx","December 2022/File2.xlsx","November 
2022/File1.xlsx","November 2022/File2.xlsx")

My final list should not include those October 2022 files because it was not included in the first one.

CodePudding user response：

We can use grep by pasteing the values in the first vector (v1) as a single pattern to match and subset the values from the main vector 'v2'

grep(paste(v1, collapse = "|"), v2, value = TRUE)

-output

[1] "December 2022/File1.xlsx" "December 2022/File2.xlsx" 
[3] "November 2022/File1.xlsx" "November 2022/File2.xlsx"

Or remove the substring suffix from second vector, create a logical vector with %in% to subset the 'v2'

v2[trimws(v2, whitespace = "/.*") %in% v1]

-output

[1] "December 2022/File1.xlsx" "December 2022/File2.xlsx"
[3] "November 2022/File1.xlsx" "November 2022/File2.xlsx"

CodePudding user response：

We could Vectorize grepl and use it in outer.

l2[colSums(outer(l1, l2, Vectorize(grepl))) > 0]
# [1] "December 2022/File1.xlsx" "December 2022/File2.xlsx"
# [3] "November 2022/File1.xlsx" "November 2022/File2.xlsx"

CodePudding user response：

Another option using "anonymous" Vectorize with grep

as.vector(Vectorize(\(x) grep(x, list1, value=T))(val))
[1] "December 2022/File1.xlsx" "December 2022/File2.xlsx"
[3] "November 2022/File1.xlsx" "November 2022/File2.xlsx"

which is close to sapply and grep

as.vector(sapply(val, grep, list1, value=T))
[1] "December 2022/File1.xlsx" "December 2022/File2.xlsx"
[3] "November 2022/File1.xlsx" "November 2022/File2.xlsx"

Data

val <- c("December 2022","November 2022")
list1 <- c("December 2022/File1.xlsx","December 2022/File2.xlsx","October 2022/File1.xlsx",
"October 2022/File2.xlsx","November 2022/File1.xlsx","November 2022/File2.xlsx")