Replace values in data frame with other values according to a rule

Question

I am an beginner in R and don`t find a solution for the following problem. Any help would be really appreciated!

I have a data.frame and want to replace certain values of a column with defined other values.

data.frame

date<-c("19921231","19931231","19941231","19941231","19931231","19941231")
variable<-c("a","a","a","b","b","b")
value<-c(1:6)
dataframe <- data.frame(date,variable,value)

attempt to solve problem

yearend<-c("19921231","19931231","19941231")
year<-c("1992","1993","1994")
map = setNames(yearend,year)
dataframe[] = map[dataframe]

error message

Error in map[dataframe] : invalid subscript type 'list'

The problem is obviously, that it is not a matrix. What is the most efficient way to solve this problem? It should also work if I want to replace "real" character, e.g. "BGSFDS" with "BASF stock".

Answer 1

A nice function is mapvalues() from the plyr package:

require(plyr)
dataframe$newdate <- mapvalues(dataframe$date, 
          from=c("19921231","19931231","19941231"), 
          to=c("1992","1993","1994"))

Answer 2

merge() might also be of help.

yearend<-c("19921231","19931231","19941231")
year<-c("1992","1993","1994")
map = data.frame(yearend,year)

merge(dataframe,map,by.x='date',by.y='yearend')