CODEWITHSUNDEEP
rerror-handlingintegertry-catch
Roman Luštrik
Roman Luštrik

Reputation: 70653

How to catch integer(0)?

Let's say we have a statement that produces integer(0), e.g.

 a <- which(1:3 == 5)

What is the safest way of catching this?

Upvotes: 173

Views: 156104

Answers (8)

James
James

Reputation: 66844

Inspired by Andrie's answer, you could use identical and avoid any attribute problems by using the fact that it is the empty set of that class of object and combine it with an element of that class:

attr(a, "foo") <- "bar"

identical(1L, c(a, 1L))
#> [1] TRUE

Or more generally:

is.empty <- function(x, mode = NULL){
    if (is.null(mode)) mode <- class(x)
    identical(vector(mode, 1), c(x, vector(class(x), 1)))
}

b <- numeric(0)

is.empty(a)
#> [1] TRUE
is.empty(a,"numeric")
#> [1] FALSE
is.empty(b)
#> [1] TRUE
is.empty(b,"integer")
#> [1] FALSE

Upvotes: 8

tjebo
tjebo

Reputation: 23767

another option is rlang::is_empty (useful if you're working in the tidyverse)

The rlang namespace does not seem to be attached when attaching the tidyverse via library(tidyverse) - in this case you use purrr::is_empty, which is just imported from the rlang package.

By the way, rlang::is_empty uses user Gavin's approach.

rlang::is_empty(which(1:3 == 5))
#> [1] TRUE

Upvotes: 2

E Nord
E Nord

Reputation: 41

You can easily catch integer(0) with function identical(x,y)

x = integer(0)
identical(x, integer(0))
[1] TRUE

foo = function(x){identical(x, integer(0))}
foo(x)
[1] TRUE

foo(0)
[1] FALSE

Upvotes: 4

Alex Yahiaoui Martinez
Alex Yahiaoui Martinez

Reputation: 1004

isEmpty() is included in the S4Vectors base package. No need to load any other packages.

a <- which(1:3 == 5)
isEmpty(a)
# [1] TRUE

Upvotes: 0

Richie Cotton
Richie Cotton

Reputation: 121127

If it's specifically zero length integers, then you want something like

is.integer0 <- function(x)
{
  is.integer(x) && length(x) == 0L
}

Check it with:

is.integer0(integer(0)) #TRUE
is.integer0(0L)         #FALSE
is.integer0(numeric(0)) #FALSE

You can also use assertive for this.

library(assertive)
x <- integer(0)
assert_is_integer(x)
assert_is_empty(x)
x <- 0L
assert_is_integer(x)
assert_is_empty(x)
## Error: is_empty : x has length 1, not 0.
x <- numeric(0)
assert_is_integer(x)
assert_is_empty(x)
## Error: is_integer : x is not of class 'integer'; it has class 'numeric'.

Upvotes: 25

IRTFM
IRTFM

Reputation: 263451

if ( length(a <- which(1:3 == 5) ) ) print(a)  else print("nothing returned for 'a'") 
#[1] "nothing returned for 'a'"

On second thought I think any is more beautiful than length(.):

 if ( any(a <- which(1:3 == 5) ) ) print(a)  else print("nothing returned for 'a'") 
 if ( any(a <- 1:3 == 5 ) ) print(a)  else print("nothing returned for 'a'")

Upvotes: 7

mbq
mbq

Reputation: 18628

Maybe off-topic, but R features two nice, fast and empty-aware functions for reducing logical vectors -- any and all:

if(any(x=='dolphin')) stop("Told you, no mammals!")

Upvotes: 13

Gavin Simpson
Gavin Simpson

Reputation: 174863

That is R's way of printing a zero length vector (an integer one), so you could test for a being of length 0:

R> length(a)
[1] 0

It might be worth rethinking the strategy you are using to identify which elements you want, but without further specific details it is difficult to suggest an alternative strategy.

Upvotes: 192

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