How to fill NA with median?

Question

Example data:

set.seed(1)
df <- data.frame(years=sort(rep(2005:2010, 12)), 
                 months=1:12, 
                 value=c(rnorm(60),NA,NA,NA,NA,         


        

Answer 1

This is a way using plyr, it is not very pretty but I think it does what you want:

library("plyr")

# Make a separate dataframe with month as first column and median as second:
medDF <- ddply(df,.(months),summarize,median=median(value,na.rm=TRUE))

# Replace `NA` values in `df$value` with medians from the second data frame
# match() here ensures that the medians are entered in the correct elements.
df$value[is.na(df$value)] <- medDF$median[match(df$months,medDF$months)][is.na(df$value)]