矩阵分配在lapply内失败 [英] matrix assignment failing within lapply
问题描述
我有一个带字符数据的data.frame,我想以一个矩阵组成,该矩阵具有相同的列标题,但每个值都有计数.到目前为止,我可以得到一个我想要的尺寸的空矩阵,但是当我尝试用计数填充 myMatrix
时,它不起作用.
I have a data.frame with character data, I want to end up with a matrix with the same column headings but with counts for each value. So far I can get an empty matrix of the dimensions I want, but when I try to populate myMatrix
with counts, it doesn't work.
myData <- data.frame(a=LETTERS[5:8], b=LETTERS[6:9], c=rep(LETTERS[5:6],2), d=rep(LETTERS[7],4))
# a b c d
# 1 E F E G
# 2 F G F G
# 3 G H E G
# 4 H I F G
myValues <- sort(unique(unlist(myData))) # E F G H I
myList <- lapply(myData, table)
myMatrix <- matrix(nrow=length(myValues), ncol=length(myList), dimnames=list(myValues,names(myList)))
# a b c d
# E NA NA NA NA
# F NA NA NA NA
# G NA NA NA NA
# H NA NA NA NA
# I NA NA NA NA
到目前为止,一切都很好.这部分没有达到我的期望:
So far so good. This is the part that doesn't do what I expect:
lapply(seq_along(myList), function(i) {myMatrix[names(myList[[i]]),names(myList[i])] <- myList[[i]]})
它返回正确的值,但是 myMatrix
仍然充满NA.奇怪的是,这一作品:
It returns the right values, but myMatrix
is still full of NAs. Oddly, this one works:
myMatrix[names(myList[[2]]),names(myList[2])] <- myList[[2]]
# a b c d
# E NA NA NA NA
# F NA 1 NA NA
# G NA 1 NA NA
# H NA 1 NA NA
# I NA 1 NA NA
为什么 myMatrix
的分配在 lapply
中失败,并且如何使它工作(没有 for
循环)?
Why is the assignment to myMatrix
failing within lapply
and how can I get it to work (without a for
loop)?
推荐答案
@orizon关于为什么您对 lapply
的使用无法按预期工作的说法是正确的.您必须将<-
替换为<<-
才能正常工作,但通常认为 * apply
不好的做法具有这种副作用.
@orizon is correct about why your use of lapply
is not working as you expected. You would have to replace <-
with <<-
for it to work but it is in general considered bad practice for *apply
functions to have such side-effects.
相反,您可以使用
sapply(lapply(myData, factor, unique(unlist(myData))), table)
# a b c d
# E 1 0 2 0
# F 1 1 2 0
# G 1 1 0 4
# H 1 1 0 0
# I 0 1 0 0
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