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 valu

Answer 1

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')

Answer 2

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 3

You can use match:

dataframe <- transform(dataframe, Year = year[match(date, yearend)])

      date variable value Year
1 19921231        a     1 1992
2 19931231        a     2 1993
3 19941231        a     3 1994
4 19941231        b     4 1994
5 19931231        b     5 1993
6 19941231        b     6 1994

Answer 4

When you want to extract the year from the date, you can do this with the following line of code:

dataframe$year <- substr(dataframe$date,1,4)

When you want assign a class to the new variable simulataniously:

dataframe$year <- as.integer(substr(dataframe$date,1,4))