问题
Complicated title but here is a simple example of what I am trying to achieve:
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\"))
Values in d$v2 should be replaced by values in m$v4 by matching the values from d$v2 in m$v3
The resulting data frame d should look like:
v1 v4
1 a
2 e
3 c
4 b
5 b
6 c
7 a
8 e
I tried different stuff and the closest I came was: d$v2 <- m$v4[which(m$v3 %in% d$v2)]
I try to avoid any for-loops again! Must be possible :-) somehow... ;)
回答1:
You could try:
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
Edit
Here is another approach, to preserve the order:
data.frame(v1=d$v1, v4=m[match(d$v2, m$v3), 2])
v1 v4
1 1 a
2 2 e
3 3 c
4 4 b
5 5 b
6 6 c
7 7 a
8 8 e
回答2:
You could use a standard left join.
Loading the data:
d <- data.frame(v1 = c(1,2,3,4,5,6,7,8), v2 = c("A","E","C","B","B","C","A","E"), stringsAsFactors=F)
m <- data.frame(v3 = c("D","E","A","C","D","B"), v4 = c("d","e","a","c","d","b"), stringsAsFactors=F)
Changing column name, such that I can join by column "v2"
colnames(m) <- c("v2", "v4")
Left joining and maintaining the order of data.frame d
library(dplyr)
left_join(d, m)
Output:
v1 v2 v4
1 1 A a
2 2 E e
3 3 C c
4 4 B b
5 5 B b
6 6 C c
7 7 A a
8 8 E e
回答3:
This will give you the desired output:
d$v2 <- m$v4[match(d$v2, m$v3)]
match function returns the position from m matrix's v3 column for the values in d$v2 being matched. Once you have obtained the indices (from using match()), access elements from m$v4 using those indices to replace the elements in d matrix, column v2.
来源：https://stackoverflow.com/questions/11530184/match-values-in-data-frame-with-values-in-another-data-frame-and-replace-former