[R] Doing a Task Without Using a For Loop

[Dimitris Rizopoulos]

try the following:

out <- tapply(data1$ID, list(data1$ID, data1$Year), length)
out[is.na(out)] <- 0
out


I hope it helps.

Best,
Dimitris


Tom La Bone wrote:
> 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
> 
> 
> 

-- 
Dimitris Rizopoulos
Assistant Professor
Department of Biostatistics
Erasmus Medical Center

Address: PO Box 2040, 3000 CA Rotterdam, the Netherlands
Tel: +31/(0)10/7043478
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