[R] Recoding lists of categories of a variable

S Ellison S.Ellison at LGCGroup.com
Tue Oct 11 01:32:08 CEST 2016

> Well, I think that's kind of overkill.
Depends whether you want to recode all or some, and how robust you want the answer to be. 
recode() allows you to recode a few levels of many, without dependence on level ordering; that's kind of neat. 

tbh, though,  I don't use recode() a lot; I generally find myself need to change a fair proportion of level labels. 

But I do get nervous about relying on specific ordering; it can break without visible warning if the data change (eg if you lose a factor level with a slightly different data set, integer indexing will give you apparently valid reassignment to the wrong new codes).  So I tend to go via named vectors even if it costs me a lot of typing. For example to change 
lcase<-c('a', 'b', 'c') 

to c('B', 'A', 'C') I'll use something like 

c(a='B', b='A', c='C')[lcase] 

or, if lcase were a factor, 
c(a='B', b='A', c='C')[as.character(lcase)] 

Unlike using the numeric levels, that doesn't fail if some of the levels I expect are absent; it only fails (and does so visibly) when there's a value in there that I haven't assigned a coding to. So it's a tad more robust.

Steve E

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