CODEWITHSUNDEEP
rdataframe
Valeria Lobos Ossandón
Valeria Lobos Ossandón

Reputation: 331

Return value of a row by specifying column index with R

I have the following dataframe (DF_A):

PARTY_ID O1 O2 O3 O4
P1  0  0 1 0
P2  2  1 0 1
P3  0  0 0 0
P4  2  1 1 1
P5  1  0 0 1

I also have another dataframe (DF_B) with the position of the columns that I need in DF_A. This is DF_B:

PARTY_ID POS_1 POS_2
P1  1  2
P2  2  1
P3  3  1
P4  2  1
P5  1  4

I need to give the position of the columns (DF_B) for getting the values of DF_A. The desired result is something like this:

PARTY_ID V1 V2
P1 0 0
P2 1 2
P3 0 0
P4 1 2
P5 1 1

I'm trying to use which function, but it seems not to work. Can anyone please help me?

SIDE NOTE: I need to do this the fastest way possible because my real data have more than 100K rows.

Upvotes: 2

Views: 1062

Answers (3)

Mankind_2000
Mankind_2000

Reputation: 2218

The one with a simple for loop:

 DF_C <- DF_B        # creating dataframe with same dimension and column/row identifiers

 for(i in 1:nrow(DF_C)) { DF_C[i,] <- DF_A[i,as.numeric(DF_B[i,])] }         #over rows

Upvotes: 1

Jilber Urbina
Jilber Urbina

Reputation: 61214

> ind <- as.matrix(DF_B[,-1])
> t(sapply(1:nrow(ind), function(i) DF_A[, -1][, ind[i,]][i,] ))
     O1 O2
[1,] 0  0 
[2,] 1  2 
[3,] 0  0 
[4,] 1  2 
[5,] 1  1

If you want to get a data.frame:

> DF <- t(sapply(1:nrow(ind), function(i) DF_A[, -1][, ind[i,]][i,] ))
> data.frame(PARTY_ID=DF_A[,1], DF)
  PARTY_ID O1 O2
1       P1  0  0
2       P2  1  2
3       P3  0  0
4       P4  1  2
5       P5  1  1

Upvotes: 1

GordonShumway
GordonShumway

Reputation: 2056

A quick and dirty way to do this using apply from base R: 

DF_C <- apply(DF_A, 1, function(x) {
  cols_to_use <- as.numeric(unlist(DF_B[DF_B$"PARTY_ID"==x["PARTY_ID"],2:3]))
  x[-1][cols_to_use]
}) 
DF_C <- cbind(DF_A$PARTY_ID,t(DF_C))
colnames(DF_C) <- c("PARTY_ID", "V1","V2")

Upvotes: 1

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