[R] how to handle a longitudinal data

[Chuck Cleland]

gallon li wrote:
> i have a data set with repeated measures on same people, structure like
> below:
> 
> id x1 x2 ...
> 001 10 20 ...
> 001 8 45 ...
> 001 4 2 ...
> 002 ....
> 002 ...
> 002 ....
> 002 ....
> 003 ....
> .......
> 
> what is the easist way to show how many observations for each subject id?

  If the data are in a data frame called df, do the following:

table(df$id)

  Also, the following is useful for seeing how many people have a
particular number of observations:

table(table(df$id))

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Chuck Cleland, Ph.D.
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