Select rows with identical columns from a data frame

Question

I have a data frame with several columns. I want to select the rows with no NAs (as with complete.cases) and all columns identical. E.g., for

> f <- data.frame(a=c(1,NA,NA,4),b=c(1,NA,3,40),c=c(1,NA,5,40))
> f
   a  b  c
1  1  1  1
2 NA NA NA
3 NA  3  5
4  4 40 40

I want the vector TRUE,FALSE,FALSE,FALSE selecting just the first row because there all 3 columns are the same and none is NA.

I can do

Reduce("==",f[complete.cases(f),])

but that creates an intermediate data frame which I would love to avoid (to save memory).

Answer 1

Try this:

R > index <- apply(f, 1, function(x) all(x==x[1]))
R > index
[1]  TRUE    NA NA FALSE
R > index[is.na(index)] <- FALSE
R > index
[1]  TRUE FALSE FALSE FALSE