Extract unique numbers from a list with multiple items per line using gsub()?-CodePudding

List A1 structured like this:

#[[1]] [1] "12" "1"

#[[2]] [1] "13" "1"

#[[3]] [1] "14" "2"

#[[4]] [1] "15" "2"

#[[5]] [1] "16" "1"

#[[6]] [1] "18" "2"

#[[7]] [1] "20" "0"

#[[8]] [1] "21" "2"

#[[9]] [1] "21" "4"

#[[10]] [1] "34" "1" "0"

#[[11]] [1] "42" "1" "1"

#[[12]] [1] "42" "2" "2"

and I'm trying to extract the unique values in the first item of each list element (for example, the number 12 in [[1]]).

When I use v <- unique(gsub( " .*$", "", A1))

the resulting vector v looks like

"c("12"," "c("13"," "c("14"," "c("15"," "c("16"," "c("18"," "c("20"," "c("21"," "c("34"," "c("42","

The desired result would be (12, 13, 14, 15, 16, 17, 18, 20, 21, 34, 42)

How do I get rid of the additional characters, where do they come from?

Thank you in advance!

CodePudding user response：

You can use

v <- list(c("12", "1"), c("13", "1"), c("12", "3"))
unique(sapply(v, "[[", 1))
# => [1] "12" "13"

Note: