Match values in data frame with values in another data frame and replace former with a corresponding pattern from the other data frame

Question

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... ;)

Answer 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