[R] which

[Chuck Cleland]

 > which(x < 5 & x > 2)
[1] 3 4

 From the help page for Logical Operators:

?"!"

      '&' and '&&' indicate logical AND and '|' and '||' indicate
      logical OR.  The shorter form performs elementwise comparisons in
      much the same way as arithmetic operators.  The longer form
      evaluates left to right examining only the first element of each
      vector.  Evaluation proceeds only until the result is determined.
      The longer form is appropriate for programming control-flow and
      typically preferred in 'if' clauses.

Y. C. Tao wrote:
> Why the last "which" in the following example doesn't
> work? Is there a simple way to identify the indices of
> array elements that meet multiple criteria?
> 
> Thanks.
> 
> YC Tao
> 
> 
>>x<-1:10
>>which(x<5)
> 
> [1] 1 2 3 4
> 
>>which(x>2)
> 
> [1]  3  4  5  6  7  8  9 10
> 
>>which(x<5 && x>2)
> 
> numeric(0)

-- 
Chuck Cleland, Ph.D.
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