It works. Thanks Jim. I guess this will be a "lots of coffee" morning kinda day.

jim holtman <jholtman@gmail.com> wrote: What exactly are you trying to do?  In the first case you are making a logical comparison and that is legal for "&".  In the second you are trying to do a logical operation ("&") between two factors and that operation is not defined.  This is what the error message is saying.
   
 Also you first attempt is probably missing a comma:
  
  node1  <- data.trt[data.trt$stage=="1B" &  data.trt$diameter=="=< 4", ]



 On Wed, Jun 4, 2008 at 8:10 AM, Philip Twumasi-Ankrah <nana_kwadwo_derkyi@yahoo.com> wrote:
 I am trying to define groupings from levels of factor variables and this the warning message that R give
 
 "& not meaningful for factors".

The nature of my task is this. I have a variable stage which has the levels (1B, 2A, 2B) - these are the AJCC TNM stages of cancer, and another variable diameter with factor levels ("=< 4", "4 - 6.5, > 6.5; limit values are exclusive).
 
I am trying to define series of groupings based on these variables and others like them.

My first attempts were;

1. node1  <- data.trt[data.trt$stage=="1B" &  data.trt$diameter=="=< 4"]
 2.  data.trt$stage[data.trt$stage=="1B"]& data.trt$diameter[data.trt$diameter=="=< 4"]

The second attempt was purely a fishing exercise.

R gave me the waring message:

Warning message:
 In Ops.factor(data.trt$stage[data.trt$stage == "1B"], data.trt$diameter[data.trt$diameter ==  :
 & not meaningful for factors


My question is how do I get round this and by implication is there an alternative way of defining a logical operation applicable to factors.
 
Thanks already for the help.

Philip


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Jim Holtman
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What is the problem you are trying to solve?  


A Smile costs Nothing  

     But Rewards Everything

Happiness is not perfected until it is shared
                                                              -Jane Porter        


       
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