# [R] Efficient swapping

Anthoni, Peter (IMK) peter.anthoni at kit.edu
Fri Jul 7 10:42:18 CEST 2017

```how about gdata functions?

set.seed(1)
(tmp <- data.frame(x = 1:10, R1 = sample(LETTERS[1:5], 10, replace = TRUE), R2 = sample(LETTERS[2:6], 10, replace = TRUE)))
tmp.orig=tmp

library(gdata)
bigMap=mapLevels(x=list(factor(tmp[,"R1"]),factor(tmp[,"R2"])),combine = T,codes=FALSE)
mapLevels(tmp[,"R1"]) = bigMap
mapLevels(tmp[,"R2"]) = bigMap
dd=as.integer(tmp[,"R2"])-as.integer(tmp[,"R1"])
odd=dd%%2!=0
swap=tmp[odd,"R2"]
tmp[odd,"R2"]=tmp[odd,"R1"]
tmp[odd,"R1"]=swap

cbind(tmp,odd,tmp.orig)

cheers
Peter

> On 7. Jul 2017, at 00:54, Gang Chen <gangchen6 at gmail.com> wrote:
>
> Thanks a lot, Ista! I really appreciate it.
>
> How about a slightly different case as the following:
>
> set.seed(1)
> (tmp <- data.frame(x = 1:10, R1 = sample(LETTERS[1:5], 10, replace =
> TRUE), R2 = sample(LETTERS[2:6], 10, replace = TRUE)))
>
>   x R1 R2
>   1  C  B
>   2  B  B
>   3  C  E
>   4  E  C
>   5  E  B
>   6  D  E
>   7  E  E
>   8  D  F
>   9  C  D
>  10  A  E
>
> Notice that the factor levels between the two factors, R1 and R2,
> slide by one level; that is, factor R1 does not have level F while
> factor R2 does not have level A. I want to swap the factor levels
> based on the combined levels of the two factors as shown below:
>
> tl <- unique(c(levels(tmp\$R1), levels(tmp\$R2)))
> for(ii in 1:dim(tmp)[1]) {
>   kk <- which(tl %in% tmp[ii,'R2'], arr.ind = TRUE) - which(tl %in%
>      tmp[ii,'R1'], arr.ind = TRUE)
>   if(kk%%2!=0) { # swap the their levels between the two factors
>      qq <- tmp[ii,]\$R1
>      tmp[ii,]\$R1 <- tmp[ii,]\$R2
>      tmp[ii,]\$R2 <- qq
>  }
> }
>
>
>
> On Thu, Jul 6, 2017 at 5:16 PM, Ista Zahn <istazahn at gmail.com> wrote:
>>
>> foo <- with(list(r1 = tmp\$R1,
>>                 r2 = tmp\$R2,
>>                 swapme = (as.numeric(tmp\$R1) - as.numeric(tmp\$R2)) %% 2 != 0),
>> {
>>    tmp[swapme, "R1"] <- r2[swapme]
>>    tmp[swapme, "R2"] <- r1[swapme]
>>    tmp
>> })
>>
>> Best,
>> Ista
>>
>> On Thu, Jul 6, 2017 at 4:06 PM, Gang Chen <gangchen6 at gmail.com> wrote:
>>> Suppose that we have the following dataframe:
>>>
>>> set.seed(1)
>>> (tmp <- data.frame(x = 1:10, R1 = sample(LETTERS[1:5], 10, replace =
>>> TRUE), R2 = sample(LETTERS[1:5], 10, replace = TRUE)))
>>>
>>>    x R1 R2
>>> 1   1  B  B
>>> 2   2  B  A
>>> 3   3  C  D
>>> 4   4  E  B
>>> 5   5  B  D
>>> 6   6  E  C
>>> 7   7  E  D
>>> 8   8  D  E
>>> 9   9  D  B
>>> 10 10  A  D
>>>
>>> I want to do the following: if the difference between the level index
>>> of factor R1 and that of factor R2 is an odd number, the levels of the
>>> two factors need to be switched between them, which can be performed
>>> through the following code:
>>>
>>> for(ii in 1:dim(tmp)[1]) {
>>>   kk <- which(levels(tmp\$R2) %in% tmp[ii,'R2'], arr.ind = TRUE) -
>>> which(levels(tmp\$R1) %in% tmp[ii,'R1'], arr.ind = TRUE)
>>>   if(kk%%2!=0) { # swap the their levels between the two factors
>>>      qq <- tmp[ii,]\$R1
>>>      tmp[ii,]\$R1 <- tmp[ii,]\$R2
>>>      tmp[ii,]\$R2 <- qq
>>>  }
>>> }
>>>
>>> More concise and efficient way to do this?
>>>
>>> Thanks,
>>> Gang
>>>
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