逐行标识1列中的值，该值对应于另外两列中的相等值 [英] Identify value in 1 column corresponding to equal values in two another columns by row

问题描述

我确信我的问题很简单，但我不知道解决方案.

I am sure that my question is quite simple but I couldn't figure out the solution.

我想按行检查我的表.如果两列(V2，V3)在同一行中具有相同的值，我想提取相应列V1中的值并将其添加到我的表中.因此:

I want to check my table by rows. If two columns (V2, V3) have the same value in the same row I want to extract the value in the corresponding column V1 and add it to my table. Thus:

我的数据

m <- matrix(c(1,2,3,5,6,0,0,0,1,3,5,4,1,1,2), 5, 3) 
df1<-as.data.frame(m) 

> df1
  V1 V2 V3
1  1  0  5
2  2  0  4
3  3  0  1
4  5  1  1
5  6  3  2

我想比较V2和V3.相同的值(1,1)在第4行中，因此我想从V1获得值5.并将其写入V4.所有其他值都可以变为NA.预期结果:

I want to compare V2 and V3. The same values (1,1) are in row 4, so I want to obtain value 5 from V1. and write it to V4. All other values can become NA. Expected result:

> df1
  V1 V2 V3 V4
1  1  0  5 NA
2  2  0  4 NA
3  3  0  1 NA
4  5  1  1 5
5  6  3  2 NA

我知道我可以通过 df1 [df1 $ V2 == max(df1 $ V2)，] 选择特定的行，但是如果我只需要第一个值而不是整个行怎么办??我的if循环不起作用...

I know that I can select the specific row by df1[df1$V2 == max(df1$V2), ], but what if I need just the first value, not the whole row? My if loop doesn't work...

newcol <- vector()
for (i in 1:nrow(df1)) {
    thematch <- which(df1[,1] == max(df1[,3]))
    newcol<-thematch
} 

和 which(df1 [，2] ==(df1 [，3])，arr.ind = TRUE)返回行数，而不是V1中的值.

and which(df1[,2] == (df1[,3]), arr.ind = TRUE) returns the number of row, not the value in V1.

谢谢！

推荐答案

我想您可以做到:

df1$V4 <- with(df1, V1[ifelse(V2==V3, TRUE, NA)] )

  V1 V2 V3 V4
1  1  0  5 NA
2  2  0  4 NA
3  3  0  1 NA
4  5  1  1  5
5  6  3  2 NA

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