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?