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List:       r-help
Subject:    Re: [R] R help
From:       Ted Harding <ted.harding () wlandres ! net>
Date:       2018-03-31 15:54:05
Message-ID: 1522511645.3833.10.camel () deb2 ! fort ! knox ! uk
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     A. On Sat, 2018-03-31 at 15:45 +0200, Henri Moolman wrote:
> Could you please provide help with something from R that I find rather
> puzzling? In the small program below x[1]=1, .  .  .  , x[5]=5. R also
> finds that x[1]<=5 is TRUE. Yet when you attempt to execute while, R does
> not seem to recognize the condition. Any thoughts on why this happens?
> 
> Regards
> 
> Henri Moolman
> 
> > x=c(1,2,3,4,5)
> > x[1]
> [1] 1
> > i=1
> > x[1]<=5
> [1] TRUE
> > while(x[i]<=5){
> +     i=i+1
> + }
> Error in while (x[i] <= 5) { : missing value where TRUE/FALSE needed

If you run the following you should understand why (the only
change is to include "print(i)" in the loop, so you can see
what is happening):

  x=c(1,2,3,4,5)
  x[1]
# [1] 1
  i=1
  x[1]<=5
# [1] TRUE
  while(x[i]<=5){
  i = i+1 ; print(i)
  }
# [1] 3
# [1] 4
# [1] 5
# [1] 6
# Error in while (x[i] <= 5) { : missing value where TRUE/FALSE needed

So everything is fine so long as i <= 5 (i.e. x[i] <= 5),
but then the loop sets i = 6. and then:

  i
# [1] 6
  x[i]
# [1] NA
  x[i] <= 5
# [1] NA

Helpful?
Best wishes,
Ted.

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