R用下一个非零值替换数据帧中的零 [英] R replacing zeros in dataframe with next non zero value

问题描述

我有一个包含零值列的数据框:

I have a dataframe with a column containing zero values:

a <- 1:10
b <- c(1, 0, 0, 0, 0, -1, -1, 0, 0, 1)
df <- data.frame(a, b)
df

如何将零值替换为最后一个非零值，即 df$b 列:

How can I replace the zero values with the last non zero value ie column df$b to be:

 1,-1,-1,-1,-1,-1,-1,1,1,1

感谢您的帮助.

推荐答案

这是 zoo 的 na.locf 的一种方法.虽然这个方法在过程中确实把一些值改成了NA，但是代码很好，很轻松.

Here's one way with na.locf from zoo. Although this method does change some values to NA in the process, the code is nice and painless.

library(zoo)
na.locf(with(df, ifelse(b == 0, NA_real_, b)), fromLast = TRUE)
# [1]  1 -1 -1 -1 -1 -1 -1  1  1  1

另一种替代方法，在长向量上可能比 ifelse 更快，是

An alternative to this, and one that might be faster than ifelse on long vectors, is

na.locf(with(df, { is.na(b) <- b == 0; b }), fromLast = TRUE)
# [1]  1 -1 -1 -1 -1 -1 -1  1  1  1

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