将NA替换为具有限制的先前值 [英] Replace NA with previous value with limit

问题描述

我想用最新的非NA值替换向量中最多n个NA值.

I would like to replace up to n NA values in vector with latest non-NA value.

例如，如果:

a <- c(1,NA,NA,NA,NA,NA,2,NA,1,NA,NA,NA)
n <- 2

我想获得:

c(1,1,1,NA,NA,NA,2,2,1,1,1,NA)

n是可以用给定元素替换的最大NA值.

n is maximum number of NA values that can be replaced by given element).

我知道na.locf()函数，但是我不知道如何设置限制n.有可能做到吗?

I know na.locf() function, but I don't know how to set the limit n. Is it possible to do it?

推荐答案

以下是使用na.locf和rle

library(zoo)
r <- rle(is.na(a))
a <- na.locf(a)
is.na(a) <- sequence(r$lengths) > n & rep(r$values, r$lengths)
a
# [1]  1  1  1 NA NA NA  2  2  1  1  1 NA

因此，这里我首先计算a中元素的游程长度(包括NA条目)，然后使用na.locf替换所有NA，最后将这些元素放回到游程长度大于n的NA处.元素是NA.

So here I first computed the run lengths of elements in a (including the NA entries), then replaced all NA's using na.locf and finally turned those elements back to NA's where the run lengths were greater than n and the elements were NA.

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