[R] Counting

[William Dunlap]

> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of Ashta
> Sent: Tuesday, October 13, 2009 5:20 AM
> To: R help
> Subject: [R] Counting
> 
> *Hi all,
> *
> 
> *Assume that I have the following data set  with tow 
> variables and I want
> count the number of observation with identical values
> *
> 
> **
> 
> *x1 x2*
> 
> * 1   1 *
> 
> * 1   0 *
> 
> * 0   1*
> 
> * 0   1*
> 
> * 0   0*
> 
> * 1   1*
> 
> * 0   1
> *
> 
> 
> I want the  following output
> **
> 
> *
> *
> 
> *n1=3  # number of identical observation between x1 and x2 variables*
> 
> *n2=4  # number of different observation*

sum() converts TRUE to 1 and FALSE to 0 so the following works
   n1 <- sum(x1 == x2)
   n2 <- sum(x1 != x2)

You can also use table() to get both numbers in one vector.  In the
following I make table's input a factor (a) to make sure that both the
== and != counts are in the table even if one count is zero and (b)
to put them in the order you asked for, TRUE then FALSE:
  n12 <- table(factor(x1==x2, levels=c(TRUE,FALSE)))
  n1 <- n12[1]
  n2 <- n12[2]

If there may be missing values in the data then you have to decide how
to handle them.

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com 

> 
> 
> How do I do it in R?
> 
> 
> Thanks a lot
> 
> 
> 
> 
> **
> 
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