[R] Doing a Task Without Using a For Loop

[Tom La Bone]

Assume that I have the dataframe "data1", which is listed at the end of this
message. I want count the number of lines that each person has for each
year. For example, the person with ID=213 has 15 entries (NinYear) for 1953.
The following bit of code calculates NinYear:

for (i in 1:length(data1$ID)) {
  data1$NinYear[i] <- length(data1[data1$Year==data1$Year[i] &
    data1$ID==data1$ID[i],1]) }

This seems to work but is horribly slow (some files I am working with have
over 500,000 lines). Can anyone suggest a faster way of doing this, perhaps
a way that does not use a for loop? Thanks.

Tom

ID	Year	NinYear
209	1971	0
209	1971	0
213	1951	0
213	1951	0
213	1953	0
213	1953	0
213	1953	0
213	1953	0
213	1953	0
213	1953	0
213	1953	0
213	1953	0
213	1953	0
213	1953	0
213	1953	0
213	1953	0
213	1953	0
213	1953	0
213	1953	0
213	1954	0
213	1954	0
213	1954	0
213	1954	0
213	1954	0
213	1954	0
213	1954	0
213	1954	0
213	1954	0
213	1954	0
213	1954	0
213	1955	0
213	1955	0
234	1953	0
234	1953	0
234	1953	0
234	1953	0
234	1953	0
234	1958	0
234	1958	0
234	1965	0
234	1965	0
234	1965	0
249	1952	0
249	1952	0



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