R有条件地申请？ [英] R conditional lapply?

问题描述

我有一个数据框，例如

a = c(2,NA,3,4)
b = c(NA,3,NA,NA)
c= c(5,NA,7,9)
test = data.frame(a,b,c)

> test
   a  b  c
1  2 NA  5
2 NA  3 NA
3  3 NA  7
4  4 NA  9

我只想填写test $ b中的NA值与该行的test $ a和test $ c的平均值。结果应为

I would like to fill in only NA values in test$b with the average of test$a and test$c for that row. The result should be

   a  b    c
1  2  3.5  5
2 NA  3    NA
3  3  5    7
4  4  6.5  9

我已经尝试过申请家庭，但还没有到任何地方。想要避免for循环，因为有人告诉我应该尽量避免for循环。

I have tried the apply family but haven't gotten anywhere. Would like to avoid a for loop because I am told I should try to avoid for loops.

我要说的是英语

if test$b[i] == NA, test$b[i] = (test$a[i] + test$b[i])/2
else leave test$b[i] as it is.

我确定这类问题已经回答了很多次，但是我找不到（或者识别）类似的东西。预先感谢。

I'm sure this kind of question has been answered many times but I can't find (or recognise) something analogous. Thanks in advance.

推荐答案

您可以为元素 NA中的元素创建逻辑行索引（indx） b列。通过使用除 b以外的列的 rowMeans，用该值替换 b中的NA值。 （根据@thelatemail的评论进行修改）

You can create a logical row index ('indx') for the elements that are 'NA' in the 'b' column. Use that to replace the NA values in 'b' by taking the `rowMeans of the columns other than 'b'. (Modified based on comments from @thelatemail)

indx <- is.na(test$b)
test$b[indx] <- rowMeans(test[indx,], na.rm=TRUE)

test
#   a   b  c
#1  2 3.5  5
#2 NA 3.0 NA
#3  3 5.0  7
#4  4 6.5  9

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