CODEWITHSUNDEEP
rcombinations
Melih Aran
Melih Aran

Reputation: 23

I want to combine columns with combination results

I want to combine columns with combination results. My data.frame has 4 columns with column name A, B, C and D. I want to merge them and my output will be a vector like c("B_C", "B_D", "C_D").my code is wrong and maybe it could help you, apply function is wrong.

data<-data.frame(A=c(1,2,3), B=c(4,5,6), C=c(7,8,9), D=c(10,11,12))
data

x1<-combinations(c(ncol(data)-1),2, c(2:ncol(data)))
x1


x12<-apply(x1, 1, function(x) paste0(colnames(data)[x1[x,]][1],"_", 
                                     colnames(data)[x1[x,]][2])    
)

Upvotes: 1

Views: 148

Answers (2)

GuedesBF
GuedesBF

Reputation: 9878

You can use either expand.grid() or combn()here

expand.grid will give you all combinations, and is "order-sensitive", returning both A-B and B-A as unique elements:

library(purrr)

expand.grid(names(data), names(data))%>%pmap_chr(~paste(..., sep = '-'))

 [1] "A-A" "B-A" "C-A" "D-A" "A-B" "B-B" "C-B" "D-B" "A-C" "B-C" "C-C" "D-C" "A-D" "B-D" "C-D" "D-D"

combn will return only the unique combinations, "order-insensitive" - "A-B" and "B-A" are considered the same and one is dropped.:

library(purrr)

data.frame(t(combn(names(data), 2)))%>%pmap_chr(~paste(..., sep = '-'))

[1] "A-B" "A-C" "A-D" "B-C" "B-D" "C-D"

Upvotes: 1

tacoman
tacoman

Reputation: 947

I'd go with sapply.

library(gtools)
data<-data.frame(A=c(1,2,3), B=c(4,5,6), C=c(7,8,9)  , D=c(10,11,12))
data

x1<-combinations(c(ncol(data)-1),2, c(2:ncol(data)))
x1
     [,1] [,2]
[1,]    2    3
[2,]    2    4
[3,]    3    4


x12 <- sapply(1L:nrow(x1), function(x) paste(colnames(data[x1[x,1L:2L]]), collapse = "_"))
x12

[1] "B_C" "B_D" "C_D"

Upvotes: 1

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