CODEWITHSUNDEEP
rif-statementna
user1700890
user1700890

Reputation: 7730

logical(0) in if statement

This line: 

which(!is.na(c(NA,NA,NA))) == 0

produces logical(0)

While this line

if(which(!is.na(c(NA,NA,NA))) == 0){print('TRUE')}

generates:

Error in if (which(!is.na(c(NA, NA, NA))) == 0) { : 
  argument is of length zero

Why there is an error? What is logical(0)

Upvotes: 27

Views: 57333

Answers (4)

Eugene Brown
Eugene Brown

Reputation: 4352

logical(0) is a vector of base type logical with 0 length. You're getting this because your asking which elements of this vector equal 0:

> !is.na(c(NA, NA, NA))
[1] FALSE FALSE FALSE
> which(!is.na(c(NA, NA, NA))) == 0
logical(0)

In the next line, you're asking if that zero length vector logical(0) is equal to 0, which it isn't. You're getting an error because you can't compare a vector of 0 length with a scalar.

Instead you could check whether the length of that first vector is 0:

if(length(which(!is.na(c(NA,NA,NA)))) == 0){print('TRUE')}

Upvotes: 29

stevec
stevec

Reputation: 52428

Simply use length() like so:

foo <- logical(0)

if(length(foo) == 0) { } # TRUE
if(length(foo) != 0) { } # FALSE

Upvotes: 5

AdamO
AdamO

Reputation: 4930

Calling which to check whether a vector of logicals is all false is a bad idea. which gives you a vector of indices for TRUE values. If there are none, that vector is length-0. A better idea is to make use of any.

> any(!is.na(c(NA,NA,NA)))
FALSE

Upvotes: 8

KenHBS
KenHBS

Reputation: 7164

First off, logical(0) indicates that you have a vector that's supposed to contain boolean values, but the vector has zero length.

In your first approach, you do

!is.na(c(NA, NA, NA))
# FALSE, FALSE, FALSE

Using the which() on this vector, will produce an empty integer vector (integer(0)). Testing whether an empty set is equal to zero, will thus lead to an empty boolean vector.

In your second approach, you try to see whether the vector which(!is.na(c(NA,NA,NA))) == 0 is TRUE or FALSE. However, it is neither, because it is empty. The if-statement needs either a TRUE or a FALSE. That's why it gives you an error argument is of length zero

Upvotes: 7

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