[R] Seeing negative numbers to zero

[(Ted Harding)]

On 07-Aug-09 20:29:16, DebbieMB wrote:
> Hi,
> I am also new to R and I have a related question.  I am trying
> to set negative values in a single column of a dataframe to zero
> and I can't seem to do it.
> 
> I have tried:
> KN1<-subset(KN,select=c(5)) 
># Here I am selecting the column of the dataframe KN1 and assigning it
># the
> name KN2 - this step works
> KN2<-ifelse(KN1<=0,0,KN1) 
># Here I am trying to set negative numbers to zero and leave all other
> numbers the same - this doesn't work
> 
> Any help would be appreciated.
> 
> Thanks,
> Debbie

How about something on the lines of:

  KN1 <- data.frame(c1=c(1,-2,3,-4,5),c2=c(-1,2,-3,4,-5),c3=c(-
  KN1
  #   c1 c2 c3
  # 1  1 -1 -2
  # 2 -2  2 -1
  # 3  3 -3  0
  # 4 -4  4  1
  # 5  5 -5  2
  KN2 <- KN1
  KN2$c2 <- (KN2$c2>0)*KN2$c2  ## ** See below
  KN2
  #   c1 c2 c3
  # 1  1  0 -2
  # 2 -2  2 -1
  # 3  3  0  0
  # 4 -4  4  1
  # 5  5  0  2

The logic of the ** line is that:
1: (KN2$c2>0) is FALSE wherever (KN2$c2 <= 0), otherwise TRUE.
2: If x is a number, then TRUE*x = x and FALSE*x = 0
3: Hence (KN2$c2>0)*KN2$c2 is 0 wherever (KN2$c2 <= 0), and
   is the same as KN2$c2 wherever (KN2$c2> 0)

Does this help?
Ted.

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E-Mail: (Ted Harding) <Ted.Harding at manchester.ac.uk>
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Date: 07-Aug-09                                       Time: 22:59:42
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