将NA行替换为前一行和某些列的非NA值 [英] Replace NA row with non-NA value from previous row and certain column
问题描述
我有一个矩阵,其中行的所有列都可以具有NA.我想用上一行的非NA值和第K列替换这些NA行.
I have a matrix, where rows can have NA's for all columns. I want to replace these NA rows with previous row's non-NA value and K-th column.
例如,此矩阵:
[,1] [,2]
[1,] NA NA
[2,] NA NA
[3,] 1 2
[4,] 2 3
[5,] NA NA
[6,] NA NA
[7,] NA NA
[8,] 6 7
[9,] 7 8
[10,] 8 9
必须转换为此非NA矩阵,我们在其中使用第2列进行替换:
Must be transformed to this non-NA matrix, where we use 2-th column for replacement:
[,1] [,2]
[1,] NA NA
[2,] NA NA
[3,] 1 2
[4,] 2 3
[5,] 3 3
[6,] 3 3
[7,] 3 3
[8,] 6 7
[9,] 7 8
[10,] 8 9
我为此编写了一个函数,但是使用了循环:
I wrote a function for this, but using loop:
# replaces rows which contains all NAs with non-NA values from previous row and K-th column
na.replace <- function(x, k) {
cols <- ncol(x)
for (i in 2:nrow(x)) {
if (sum(is.na(x[i - 1, ])) == 0 && sum(is.na(x[i, ])) == cols) {
x[i, ] <- x[i - 1 , k]
}
}
x
}
似乎此功能可以正常工作,但我想避免这些循环.任何人都可以提出建议,我如何不使用循环就可以进行这种替换?
Seems this function works correct, but I want to avoid these loops. Can anyone advice, how I can do this replacement without using loops?
更新
agstudy 建议它是自己的矢量化非循环解决方案:
agstudy suggested it's own vectorized non-loop solution:
na.replace <- function(mat, k){
idx <- which(rowSums(is.na(mat)) == ncol(mat))
mat[idx,] <- mat[ifelse(idx > 1, idx-1, 1), k]
mat
}
但是,与我的带有循环的解决方案相比,该解决方案返回了不同且错误的结果.为什么会这样?理论上,循环解和非循环解是相同的.
But this solution returns different and wrong results, comparing to my solution with loops. Why this happens? Theoretically loop and non-loop solutions are identical.
推荐答案
最后,我实现了自己的矢量化版本.它返回预期的输出:
Finally I realized my own vectorized version. It returns expected output:
na.replace <- function(x, k) {
isNA <- is.na(x[, k])
x[isNA, ] <- na.locf(x[, k], na.rm = F)[isNA]
x
}
更新
更好的解决方案,无需任何软件包
Better solution, without any packages
na.lomf <- function(x) {
if (length(x) > 0L) {
non.na.idx <- which(!is.na(x))
if (is.na(x[1L])) {
non.na.idx <- c(1L, non.na.idx)
}
rep.int(x[non.na.idx], diff(c(non.na.idx, length(x) + 1L)))
}
}
na.lomf(c(NA, 1, 2, NA, NA, 3, NA, NA, 4, NA))
# [1] NA 1 2 2 2 3 3 3 4 4
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