How to check if each element in a vector is integer or not in R?

Question

Say, I have a vector y, and I want to check if each element in y is integer or not, and if not, stop with an error message. I tried is.integer(y), but it does not work.

Answer 1

The simplest (and fastest!) thing is probably this:

stopifnot( all(y == floor(y)) )

...So trying it out:

y <- c(3,4,9)
stopifnot( all(y == floor(y)) ) # OK

y <- c(3,4.01,9)
stopifnot( all(y == floor(y)) ) # ERROR!

If you want a better error message:

y <- c(3, 9, NaN)
if (!isTRUE(all(y == floor(y)))) stop("'y' must only contain integer values")

Answer 2

you could do:

   y <- c(3,3.1,1,2.3)
   (y - floor(y)) == 0
    [1]  TRUE FALSE  TRUE FALSE

or

   (y - round(y)) == 0

and if you want a single TRUE or FALSE for the whole thing, put it in all(), e.g.:

   all((y - round(y)) == 0)
    [1] FALSE

Answer 3

Here's another way (using the same trick as Justin of comparing each number to that number coerced into the 'integer' type):

R> v1 = c(1,2,3)
R> v2 = c(1,2,3.5)
R> sapply(v1, function(i) i == as.integer(i))
[1] TRUE TRUE TRUE
R> sapply(v2, function(i) i == as.integer(i))
[1]  TRUE  TRUE FALSE

To make your test:

R> all(sapply(v2, function(i) i == as.integer(i)))
[1] FALSE

Answer 4

Not sure which is faster Tim's way or this, but:

> x <- 1:5
> y <- c(x, 2.0)
> z <- c(y, 4.5)
> all.equal(x, as.integer(x))
[1] TRUE
> all.equal(y, as.integer(y))
[1] TRUE
> all.equal(z, as.integer(z))
[1] "Mean relative difference: 0.1111111"
> 

or:

all((z - as.integer(z))==0)