将数据帧中的值与另一个数据帧中的值进行匹配,并将前者替换为另一个数据帧中的相应模式

Question

复杂的标题,但这是我想要实现的一个简单的例子:

d <- data.frame(v1 = c(1,2,3,4,5,6,7,8), 
                v2 = c("A","E","C","B","B","C","A","E"))

m <- data.frame(v3 = c("D","E","A","C","D","B"), 
                v4 = c("d","e","a","c","d","b"))

在价值d$v2应该由值来代替m$v4从值相匹配d$v2的m$v3

生成的数据框d应如下所示:

v1    v4
1      a
2      e
3      c
4      b
5      b
6      c
7      a
8      e

我尝试了不同的东西,我最接近的是: d$v2 <- m$v4[which(m$v3 %in% d$v2)]

我试着再次避免任何for循环!必须是可能的:-)不知怎的......;)

Answer 1

你可以尝试:

merge(d,m, by.x="v2", by.y="v3")
  v2 v1 v4
1  A  1  a
2  A  7  a
3  B  4  b
4  B  5  b
5  C  3  c
6  C  6  c
7  E  2  e
8  E  8  e

编辑

这是保持顺序的另一种方法:

data.frame(v1=d$v1, v4=m[match(d$v2, m$v3), 2])
  v1 v4
1  1  a
2  2  e
3  3  c
4  4  b
5  5  b
6  6  c
7  7  a
8  8  e

Answer 2

您可以使用标准的左连接.

加载数据:

d <- data.frame(v1 = c(1,2,3,4,5,6,7,8), v2 = c("A","E","C","B","B","C","A","E"), stringsAsFactors=F)
m <- data.frame(v3 = c("D","E","A","C","D","B"), v4 = c("d","e","a","c","d","b"), stringsAsFactors=F)

更改列名,以便我可以按列"v2"加入

colnames(m) <- c("v2", "v4")

左连接并维护data.frame d的顺序

library(dplyr)
left_join(d, m)

输出:

  v1 v2 v4
1  1  A  a
2  2  E  e
3  3  C  c
4  4  B  b
5  5  B  b
6  6  C  c
7  7  A  a
8  8  E  e

Answer 3

这将为您提供所需的输出：

d$v2 <- m$v4[match(d$v2, m$v3)]

match 函数返回 m 矩阵的 v3 列中d$v2匹配值的位置。获得索引（通过 using match()）后，m$v4使用这些索引访问元素以替换 d 矩阵第 v2 列中的元素。