Home/ Questions/Why do I get the condition has length > 1 and only the first element will be used error?
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Aaliyah Davis
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Asked: 2022-05-11T02:19:33+00:00 In:

Why do I get the condition has length > 1 and only the first element will be used error?

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Hi developer experts,

I have a small but frustrating use case, and so far, I couldn’t get my head around this problem & ideal solution. I am running my program, and I am facing one problem with the the condition has length > 1 and only the first element will be used.

Below is the command I used:

 a <- c(0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0)
w<-function(a){
  if (a>0){
     a/sum(a)
  }
  else 1
}

when I run it, I get the following error:

  Warning message:
  In if (a > 0) { :
  the condition has length > 1 and only the first element will be used

I am looking forward to gaining some knowledge from all experts. Thank you, guys!

only the first element will be used
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3 Answers

  1. Best Answer

    The error occured because you intended to pass f() a vector with length > 1.

    In R, if() and else() can only react to one logical element (true or false) at 1 time.

    The options I might suggest you are:

    1. use sapply(t, f)

    2. or use ifelse() because ifelse() can react to a logical vector with length > 1.

    Below is my example of using ifelse()

    f <- function(t) {
    /* ifelse(condition, do_if_true, do_if_false) */
    ifelse(t < 0, 0, (2*t)/((1+t^2)^2)
}
    • 11

  2. The if statement cannot be vectorized. ifelse is recommended for vectorized if statements. It is enough to write in your case 

    w <- function(a){
if (any(a>0)){
 a/sum(a)
}
 else 1
}

    Or a shorter vectorised version 

    ifelse(a > 0, a/sum(a), 1)

    It all depends on which function you use. First function produces an output vector of length 1, while ifelse generates an output vector equal to a.

    • 14

  3. Maybe you are interested in ifelse

    a <- c(1,1,1,1,0,0,0,0,2,2)
ifelse(a>0,a/sum(a),1)

 [1] 0.125 0.125 0.125 0.125 1.000 1.000 1.000 1.000
 [9] 0.250 0.250
    • 1

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