data.frame
(或 data.table
)中,我想用最近的非 NA 值填充 NA。 以下是一个简单的示例,使用向量(而不是 data.frame
):> y <- c(NA, 2, 2, NA, NA, 3, NA, 4, NA, NA)
我希望有一个名为
fill.NAs()
的函数,可以帮助我构建yy
,使得:
> yy
[1] NA NA NA 2 2 2 2 3 3 3 4 4
我需要为许多(总共约1TB)小型数据框(约30-50MB)重复此操作,其中如果一行的所有条目都是NA,则该行为NA。有什么好的方法来解决这个问题?
我想到了一个丑陋的解决方案,使用了这个函数:
last <- function (x){
x[length(x)]
}
fill.NAs <- function(isNA){
if (isNA[1] == 1) {
isNA[1:max({which(isNA==0)[1]-1},1)] <- 0 # first is NAs
# can't be forward filled
}
isNA.neg <- isNA.pos <- isNA.diff <- diff(isNA)
isNA.pos[isNA.diff < 0] <- 0
isNA.neg[isNA.diff > 0] <- 0
which.isNA.neg <- which(as.logical(isNA.neg))
if (length(which.isNA.neg)==0) return(NULL) # generates warnings later, but works
which.isNA.pos <- which(as.logical(isNA.pos))
which.isNA <- which(as.logical(isNA))
if (length(which.isNA.neg)==length(which.isNA.pos)){
replacement <- rep(which.isNA.pos[2:length(which.isNA.neg)],
which.isNA.neg[2:max(length(which.isNA.neg)-1,2)] -
which.isNA.pos[1:max(length(which.isNA.neg)-1,1)])
replacement <- c(replacement, rep(last(which.isNA.pos), last(which.isNA) - last(which.isNA.pos)))
} else {
replacement <- rep(which.isNA.pos[1:length(which.isNA.neg)], which.isNA.neg - which.isNA.pos[1:length(which.isNA.neg)])
replacement <- c(replacement, rep(last(which.isNA.pos), last(which.isNA) - last(which.isNA.pos)))
}
replacement
}
函数fill.NAs
的用法如下:
y <- c(NA, 2, 2, NA, NA, 3, NA, 4, NA, NA)
isNA <- as.numeric(is.na(y))
replacement <- fill.NAs(isNA)
if (length(replacement)){
which.isNA <- which(as.logical(isNA))
to.replace <- which.isNA[which(isNA==0)[1]:length(which.isNA)]
y[to.replace] <- y[replacement]
}
输出
> y
[1] NA 2 2 2 2 3 3 3 4 4 4
...看起来好像能用。但是,天啊,它太丑了!有什么建议吗?
data.table
中找到了roll=TRUE
。 - Matt Dowle