[英]remove matrix from a list of matrices
I have a list of 12 matrices called M
and I'm trying to remove every matrix from the list that has 0 rows.我有一个名为M
的 12 个矩阵的列表,我试图从列表中删除每个有 0 行的矩阵。
I know that I can manually remove those matrices with (for example, to remove the second matrix) M[2] <- NULL
.我知道我可以手动删除这些矩阵(例如,删除第二个矩阵) M[2] <- NULL
。 I would like to use logic to remove them with something like: M <- M[nrow(M)>0,]
(but that obviously didn't work).我想使用逻辑来删除它们,例如: M <- M[nrow(M)>0,]
(但这显然不起作用)。
Another option that could work is Filter
in base R
另一个可以工作的选项是base R
中的Filter
Filter(nrow, M)
It works because 0 is considered as FALSE and all other values as TRUE它之所以有效,是因为 0 被视为 FALSE,所有其他值都被视为 TRUE
If there are also some attributes, gv
from collapse
could maintain it如果还有一些属性, gv
from collapse
可以保持它
library(collapse)
gv(M, function(x) nrow(x) > 0)
Use sapply()
to get a logical vector of non-zero matrices, then use that vector to select/subset:使用sapply()
获取非零矩阵的逻辑向量,然后使用该向量来选择/子集:
nzm <- sapply(M, function(m) nrow(m)>0)
M <- M[nzm]
Here is a one-liner.这是一个单线。
M <- M[sapply(M, nrow) != 0]
M <- lapply(1:5, function(n){
if(n %% 2 == 0)
matrix(nrow = 0, ncol = 2)
else
matrix(1:4, nrow = 2)
})
I think @Akrun has the cleanest answer.我认为@Akrun 有最清晰的答案。 I made this up before I saw his.这是我在看到他之前编造的。 It is reproducible and also explains a different way of going about it that I used with out thinking about more elegant solutions.它是可重现的,并且还解释了我使用的一种不同的处理方式,而没有考虑更优雅的解决方案。
# create list of matrices
matrixlist <- list(matrix(nrow=4,ncol=4,1),
matrix(nrow=4,ncol=4,1),
matrix(nrow=0,ncol=4,1),
matrix(nrow=4,ncol=4,1))
matrixlist
# Identify matrices in my list that have at least one row
idx <- lapply(lapply(matrixlist, `[`), nrow) > 0
# subset the original list with this criteria
my_revised_matrixlist <- matrixlist[idx]
my_revised_matrixlist
All this was accomplished by Akrun's simple Filter(nrow, matrixlist)
这一切都是由 Akrun 的简单Filter(nrow, matrixlist)
完成的
Another option worth mentioning with purrr
is keep()
, discard()
, or compact()
. purrr
值得一提的另一个选项是keep()
、 discard()
或compact()
。 The package purrr
is my go-to these days with lists. package purrr
是我最近的清单。
library(purrr)
# simplest by far
compact(M)
# probably a bit easier to remember what you did later
keep(M, ~ nrow(.) > 0)
discard(M, ~ nrow(.) == 0)
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