Impute missing data with mean by group

Question

I have a categorical variable with three levels (A, B, and C).

I also have a continuous variable with some missing values on it.

I would like to replace the NA values with the mean of its group. This is, missing observations from group A has to be replaced with the mean of group A.

I know I can just calculate each group's mean and replace missing values, but I'm sure there's another way to do so more efficiently with loops.

A <- subset(data, group == "A")
mean(A$variable, rm.na = TRUE)
A$variable[which(is.na(A$variable))] <- mean(A$variable, na.rm = TRUE)

Now, I understand I could do the same for group B and C, but perhaps a for loop (with if and else) might do the trick?

Please create a minimal working example: https://stackoverflow.com/questions/5963269/how-to-make-a-great-r-reproducible-example — emilliman5, Mar 25 '19 at 20:05

iod · Accepted Answer · 2019-03-27T12:34:07.777

9

require(dplyr)
data %>% group_by(group) %>%
mutate(variable=ifelse(is.na(variable),mean(variable,na.rm=TRUE),variable))

For a faster, base-R version, you can use ave:

data$variable<-ave(data$variable,data$group,FUN=function(x) 
  ifelse(is.na(x), mean(x,na.rm=TRUE), x))

edited Mar 27 '19 at 12:34

answered Mar 25 '19 at 20:10

iod

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just for the fun of it, added a base-R solution above. – iod Mar 27 '19 at 12:34

score 0 · Answer 2 · answered Mar 25 '19 at 20:24

0

You could use data.table package to achieve this-

tomean <- c("var1", "var2")
library(data.table)
setDT(dat)
dat[, (tomean) := lapply(tomean, function(x) {
        x <- get(x)
        x[is.na(x)] <- mean(x, na.rm = TRUE)
        x
    })]

answered Mar 25 '19 at 20:24

Rushabh Patel

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34

Impute missing data with mean by group

2 Answers2