I suggest you use the recode function in car package to do your job.
======= 2005-10-20 08:09:08 您在来信中写道：=======
>Hello,
>
>I have read through the manuals and can't seem to find an answer.
>
>I have a categorical, character variable that has hundreds of values. I want
>to group the existing values of this variable into a new, derived
>(categorical) variable by applying conditions to the values in the data.
>
>For example, suppose I have a data frame with variables: date, country, x, y,
>and z.
>
>x,y,z are numeric and country is a 2-digit character string. I want to create
>a new derived variable named "continent" that would also exist in the data
>frame. The Continent variable would have values of "Asia", "Europe", "North
>America", etc...
>
>How would this best be done for a large dataset (>10MB) ?
>I have tried many variations on following without success (note in a real
>example I would have a longer list of countries and continent values):
>
>> mydata$continent <- mydata[ mydata$country==list('US','CA','MX'), ] ->
>> "North America"
>
>I have read about factors, but I am not sure how they apply here.
>
>Can anyone help me with the syntax? I am sure it is trivial and a common
>thing to do.
>The ultimate goal is to compute percentages of x by continent.
>
>Thanks for any help in advance.
>
>-Avram
>
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2005-10-20
------
Deparment of Sociology
Fudan University
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