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I'm trying to extract the second subelement of every element in a list while ignoring NAs in R. Here's a small example:
mylist <- list(a=c(6,7),b=NA,c=c(8,9))
sapply(mylist, "[[", 1)
sapply(mylist, "[[", 2) #receive error
Because element 'b' has only one subelement (NA), I receive the following error when trying to extract the second subelement:
Error in FUN(X[[2L]], ...) : subscript out of bounds
My goal is for the output to be: 7, NA, 9. In other words, I want to ignore and retain the NAs so that the output is the same length as the number of elements in the list. I would like the solution to be general enough to also be able to apply it to a different subelement, n, from each list.
544
To extract only first element from a list, we can use sapply function and access the first element with double square brackets. For example, if we have a list called LIST that contains 5 elements each containing 20 elements then the first sub-element can be extracted by using the command sapply(LIST,"[[",1).
This should do what you want:
sapply(mylist,function(x) x[2])
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