[R] Changing multiple instances in data.frame

[David Winsemius]

On Mar 28, 2012, at 6:40 PM, Trevor Davies wrote:

> Thank you, works perfectly.
>

Good. There is also a recode function in package 'car' (IIRC) which  
attempts to replicate the syntax of the same command in SPSS. But once  
I figured out how to use match() as an index with "[", I have never  
needed to use that method. (Which is not to say that I am not in debt  
to John Fox... his scatter3d functions is a real gem.)

-- 
david.

> On Wed, Mar 28, 2012 at 3:11 PM, David Winsemius <dwinsemius at comcast.net 
> >wrote:
>
>>
>> On Mar 28, 2012, at 5:26 PM, Trevor Davies wrote:
>>
>> I've looked but I cannot find a more elegant solution.
>>>
>>> I would like to be able to scan through a data.frame and remove  
>>> multiple
>>> and various instances of certain contents.
>>>
>>> A trivial example is below.  It works, it just seems like there  
>>> should be
>>> a
>>> one line solution.
>>>
>>> #Example data:
>>> a <-
>>> data.frame(V1=1:3,V2=c(paste(**LETTERS[1],LETTERS[1:3],sep=''**
>>> )),options(stringsAsFactors
>>> = FALSE))
>>>
>>> #> a
>>> # V1 V2
>>> #1  1 AA
>>> #2  2 AB
>>> #3  3 AC
>>>
>>> #Cumbersome solution (which would be even more cumbersome with  
>>> real data)
>>>
>>> indices.of.aa <- which(a$V2 %in% "AA")
>>> indices.of.ab <- which(a$V2 %in% "AB")
>>> indices.of.ac <- which(a$V2 %in% "AC")
>>> a$V2 <- replace(a$V2, indices.of.aa, "c")
>>> a$V2 <- replace(a$V2, indices.of.ab, "d")
>>> a$V2 <- replace(a$V2, indices.of.ac, "e")
>>>
>>>
>> Use match:
>>
>>> df1 <-  
>>> data.frame(V1=1:3,V2=c(paste(**LETTERS[1],LETTERS[1:3],sep=''**
>> )),
>>                 stringsAsFactors = FALSE))
>>> unique(df1$V2)
>> [1] "AA" "AB" "AC"
>>> df1$new <- c("c","d","e")[match(df1$V2, unique(df1$V2))]
>>> df1
>> V1 V2 new
>> 1  1 AA   c
>> 2  2 AB   d
>> 3  3 AC   e
>>
>>
>>
>> ## output
>>> #> a
>>> #  V1 V2
>>> #1  1  c
>>> #2  2  d
>>> #3  3  e
>>>
>>> I know with the trivial example above there are extremely simple  
>>> solutions
>>> but my data.frame is a few thousand rows.
>>> Thanks all.
>>> Trevor
>>>
>>>       [[alternative HTML version deleted]]
>>>
>>
>>
>> ---
>> David Winsemius, MD
>> West Hartford, CT
>>
>>
>
> 	[[alternative HTML version deleted]]
>
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David Winsemius, MD
West Hartford, CT