I have very big list, but some of the elements(positions) are NULL, means nothing inside there. I want just extract the part of my list, which is non-empty. Here is my effort, but I faced with error:
ind<-sapply(mylist, function() which(x)!=NULL)
list<-mylist[ind]
#Error in which(x) : argument to 'which' is not logical
Would someone help me to implement it ?
You can use the logical negation of is.null
here. That can be applied over the list with vapply
, and we can return the non-null elements with [
(mylist <- list(1:5, NULL, letters[1:5]))
# [[1]]
# [1] 1 2 3 4 5
# [[2]]
# NULL
# [[3]]
# [1] "a" "b" "c" "d" "e"
mylist[vapply(mylist, Negate(is.null), NA)]
# [[1]]
# [1] 1 2 3 4 5
# [[2]]
# [1] "a" "b" "c" "d" "e"
Try:
myList <- list(NULL, c(5,4,3), NULL, 25)
Filter(Negate(is.null), myList)
如果您不关心结果结构,可以unlist
:
unlist(mylist)
错误的含义是您的括号不正确,您要测试的条件必须在which
函数中:
which(x != NULL)
One can extract the indices of null enteries in the list using "which" function and not include them in the new list by using "-".
new_list=list[-which(is.null(list[]))]
should do the job :)
Try this:
list(NULL, 1, 2, 3, NULL, 5) %>%
purrr::map_if(is.null, ~ NA_character_) %>% #convert NULL into NA
is.na() %>% #find NA
`!` %>% #Negate
which() #get index of Non-NULLs
or even this:
list(NULL, 1, 2, 3, NULL, 5) %>%
purrr::map_lgl(is.null) %>%
`!` %>% #Negate
which()
MyList <- list(NULL, c(5, 4, 3), NULL, NULL)
[[1]]
NULL
[[2]]
[1] 5 4 3
[[3]]
NULL
[[4]]
NULL
MyList[!unlist(lapply(MyList,is.null))]
[[1]]
[1] 5 4 3
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