Create Flag Variables in R using a function

Question

I am wanting to create a function in R, that would output flag variables that are derived from the original variables in the data frame, and then ideally for every variable in the data frame.

I want to create a new variable for each variable in the data frame, and the value would be equal to 1 if the original variable value is NA, or it would be equal to 0 if not NA.

I also want to call the new variable the same thing as the original variable, except with the prefix of "M_" before it.

Here is an example:

INDEX   HEIGHT    LENGTH
1       70        55
2       60        NA
3       NA        35
4       NA        NA

I would want the output to look like this:

INDEX   HEIGHT  M_HEIGHT  LENGTH  M_LENGTH
1       70      0         55      0
2       60      0         NA      1
3       NA      1         35      0
4       NA      1         NA      1

I am currently doing this for each variable individually, but I want to speed things up and not have to repeat the same thing over and over.

df$M_HEIGHT <- ifelse(is.na(HEIGHT),1,0)

Answer 1

The "[<-" function can create (assign) new columns by name:

> dat[ , paste0( "M_",names(dat)[-1])] <- 
       lapply(dat[-1], function(x) as.numeric(is.na(x)) )
> dat
  INDEX HEIGHT LENGTH M_HEIGHT M_LENGTH
1     1     70     55        0        0
2     2     60     NA        0        1
3     3     NA     35        1        0
4     4     NA     NA        1        1

Since you wanted to assign the expected 0/1 values for the is.na logical test there was no need for an ifelse. You could have used ifelse if there were a more complex test or value range.