list 从带有字符（0）的列表中删除空元素
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Remove empty elements from list with character(0)
提问by Richard A. Sch?fer
How can I remove empty elements from a list that contain zero length pairlist as
character(0), integer(0)etc...
我怎样才能把包含零长度的成对列表为空表元素
character(0)，integer(0)等等......
list2
# $`hsa:7476`
# [1] "1","2","3"
#
# $`hsa:656`
# character(0)
#
# $`hsa:7475`
# character(0)
#
# $`hsa:7472`
# character(0)
I don't know how to deal with them. I mean if NULLit is much simpler. How can I remove these elements such that just hsa:7476remains in the list.
我不知道怎么对付他们。我的意思是如果NULL它更简单。如何删除这些元素，使其仅hsa:7476保留在列表中。
回答by agstudy
Another option(I think more efficient) by keeping index where element length > 0 :
另一种选择（我认为更有效）通过保持元素长度 > 0 的索引：
l[lapply(l,length)>0] ## you can use sapply,rapply
[[1]]
[1] 1 2 3
[[2]]
[1] "foo"
回答by Julius Vainora
One possible approach is
一种可能的方法是
Filter(length, l)
# [[1]]
# [1] 1 2 3
#
# [[2]]
# [1] "foo"
where
在哪里
l <- list(1:3, "foo", character(0), integer(0))
This works due to the fact that positive integers get coerced to TRUEby Filterand, hence, are kept, while zero doesn't:
该工程由于这样的事实，正整数得到强制为TRUE通过Filter，因此，被保留，而零不：
as.logical(0:2)
# [1] FALSE TRUE TRUE
回答by lukeA
For the sake of completeness, the purrrpackage from the popular tidyversehas some useful functions for working with lists - compact(introduction) does the trick, too, and works fine with magrittr's %>%pipes:
为了完整起见，流行的tidyverse 中的purrr包有一些有用的函数来处理列表 - （介绍）也可以解决这个问题，并且可以很好地与 magrittr 的管道配合使用：compact%>%
l <- list(1:3, "foo", character(0), integer(0))
library(purrr)
compact(l)
# [[1]]
# [1] 1 2 3
#
# [[2]]
# [1] "foo"
or
或者
list(1:3, "foo", character(0), integer(0)) %>% compact
回答by Artem Klevtsov
Use lengths()to define lengths of the list elements:
使用lengths()定义列表元素的长度：
l <- list(1:3, "foo", character(0), integer(0))
l[lengths(l) > 0L]
#> [[1]]
#> [1] 1 2 3
#>
#> [[2]]
#> [1] "foo"
#>
回答by not2qubit
Funny enough, none of the many solutions above remove the empty/blank character string: "". But the trivial solution is not easily found: L[L != ""].
有趣的是，上面的许多解决方案都没有删除空/空白字符串："". 但并不容易找到微不足道的解决方案：L[L != ""].
To summarize, here are some various ways to remove unwanted items from an array list.
总而言之，这里有一些从数组列表中删除不需要的项目的各种方法。
# Our Example List:
L <- list(1:3, "foo", "", character(0), integer(0))
# 1. Using the *purrr* package:
library(purrr)
compact(L)
# 2. Using the *Filter* function:
Filter(length, L)
# 3. Using *lengths* in a sub-array specification:
L[lengths(L) > 0]
# 4. Using *lapply* (with *length*) in a sub-array specification:
L[lapply(L,length)>0]
# 5. Using a sub-array specification:
L[L != ""]
# 6. Combine (3) & (5)
L[lengths(L) > 0 & L != ""]
