Replace missing values (NA) in one data set with values from another where columns match

问题

I have a data frame (datadf) with 3 columns, 'x', 'y, and z. Several 'x' values are missing (NA). 'y' and 'z' are non measured variables.

x    y z
153  a 1
163  b 1
NA   d 1
123  a 2 
145  e 2
NA   c 2 
NA   b 1
199  a 2

I have another data frame (imputeddf) with the same three columns:

I wish to replace NA in 'x' in 'datadf' with values from 'imputeddf' where 'y' and 'z' matches between the two data sets (each combo of 'y' and 'z' has its own value of 'x' to fill in).

The desired result:

I am trying things like:

finaldf <- datadf
finaldf$x <- if(datadf[!is.na(datadf$x)]){ddply(datadf, x=imputeddf$x[datadf$y == imputeddf$y & datadf$z == imputeddf$z])}else{datadf$x}

but it's not working.

What is the best way for me to fill in the NA in the using my imputed value df?

回答1:

I would do this:

library(data.table)
setDT(DF1); setDT(DF2)

DF1[DF2, x := ifelse(is.na(x), i.x, x), on=c("y","z")]

which gives

Comments. This approach isn't so great, since it merges the whole of DF1, while we only need to merge the subset where is.na(x). Here, the improvement looks like (thanks, @Arun):

DF1[is.na(x), x := DF2[.SD, x, on=c("y", "z")]]

This way is analogous to @RHertel's answer.

回答2:

Here's an alternative with base R:

df1[is.na(df1$x),"x"] <- merge(df2,df1[is.na(df1$x),][,c("y","z")])$x
> df1
#    x y z
#1 153 a 1
#2 163 b 1
#3 124 b 1
#4 123 a 2
#5 145 e 2
#6 176 c 2
#7 184 d 1
#8 199 a 2

回答3:

A dplyr solution, conceptually identical to the answers above. To pull out just the rows of imputeddf that correspond to NAs in datadf, use semi_join. Then, use another join to match back to datadf. (This step is not very clean, unfortunately.)

library(dplyr)
replacement_rows <- imputeddf %>%
  semi_join(datadf %>% filter(is.na(x)), by = c("y", "z"))
datadf <- datadf %>%
  left_join(replacement_rows, by = c("y", "z")) %>%
  mutate(x = if_else(is.na(x.x), x.y, x.x)) %>%
  select(x, y, z)

This gets what you want:

> datadf
# A tibble: 8 x 3
      x y         z
  <dbl> <chr> <dbl>
1   153 a         1
2   163 b         1
3   184 d         1
4   123 a         2
5   145 e         2
6   176 c         2
7   124 b         1
8   199 a         2

来源：https://stackoverflow.com/questions/32638845/replace-missing-values-na-in-one-data-set-with-values-from-another-where-colum

标签

plyr