[R] unexpected behavior in apply

[Jiefei Wang]

Hi,

I guess this can tell you what happens behind the scene


> d<-data.frame(d1 = letters[1:3],
+               d2 = c(1,2,3),
+               d3 = c(NA,NA,6))
> apply(d, 2, FUN=function(x)x)
     d1  d2  d3
[1,] "a" "1" NA
[2,] "b" "2" NA
[3,] "c" "3" " 6"
> "a"<=3
[1] FALSE
> "2"<=3
[1] TRUE
> "6"<=3
[1] FALSE

Note that there is an additional space in the character value " 6",
that's why your comparison fails. I do not understand why but this
might be a bug in R

Best,
Jiefei

On Sat, Oct 9, 2021 at 1:49 AM Derickson, Ryan, VHA NCOD via R-help
<r-help using r-project.org> wrote:
>
> Hello,
>
> I'm seeing unexpected behavior when using apply() compared to a for loop when a character vector is part of the data subjected to the apply statement. Below, I check whether all non-missing values are <= 3. If I include a character column, apply incorrectly returns TRUE for d3. If I only pass the numeric columns to apply, it is correct for d3. If I use a for loop, it is correct.
>
> > d<-data.frame(d1 = letters[1:3],
> +               d2 = c(1,2,3),
> +               d3 = c(NA,NA,6))
> >
> > d
>   d1 d2 d3
> 1  a  1 NA
> 2  b  2 NA
> 3  c  3  6
> >
> > # results are incorrect
> > apply(d, 2, FUN=function(x)all(x[!is.na(x)] <= 3))
>    d1    d2    d3
> FALSE  TRUE  TRUE
> >
> > # results are correct
> > apply(d[,2:3], 2, FUN=function(x)all(x[!is.na(x)] <= 3))
>    d2    d3
>  TRUE FALSE
> >
> > # results are correct
> > for(i in names(d)){
> +   print(all(d[!is.na(d[,i]),i] <= 3))
> + }
> [1] FALSE
> [1] TRUE
> [1] FALSE
>
>
> Finally, if I remove the NA values from d3 and include the character column in apply, it is correct.
>
> > d<-data.frame(d1 = letters[1:3],
> +               d2 = c(1,2,3),
> +               d3 = c(4,5,6))
> >
> > d
>   d1 d2 d3
> 1  a  1  4
> 2  b  2  5
> 3  c  3  6
> >
> > # results are correct
> > apply(d, 2, FUN=function(x)all(x[!is.na(x)] <= 3))
>    d1    d2    d3
> FALSE  TRUE FALSE
>
>
> Can someone help me understand what's happening?
>
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