Suppose that you have a dataframe myData, with columns A,B,C and you want
a new column D to have the counts for each item in column A, then try:
myData$D<-table(myData$A)[as.character(myData$A)]
The table creates the counts as a named vector by converting the column to
a factor, the names are the levels.
The result is indexed into the data set by level name, here the associated
character strings for myData$A.
Should work for integers, factors and character strings,
as.character is required for numeric values of myData$A
in response to:
My data looks like this one:
A B C
1 a 1 ff
2 b 1 re
3 c 1 sd
5 a 2 as
6 c 4 fe
7 d 5 tt
8 d 5 tt
9 d 9 oi
I want to add a new column D, which will contain how many an element from
the column A is repeated, like this:
A B C D
1 a 1 ff 2
2 b 1 re 1
3 c 1 sd 2
5 a 2 as 2
6 c 4 fe 2
7 d 5 tt 3
8 d 5 tt 3
9 d 9 oi 3
Tom Jagger
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