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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