[R] Looped t.test results according to a subset variable

[Matthew Dubins]

I've tried to use by(), but the closest i got to it doing what I wanted 
was using the following:

 by(percent, quiz, function(percent) {t.test(percent~group, 
data=marks.long)})

But the results it gave me weren't t.tests of percent by group according 
to quiz number.


Julian Burgos wrote:
> See by()
>
> Matthew Dubins wrote:
>> Hi all,
>>
>> I wrote a simple function that gives me multiple t.test results 
>> according to a subset variable and am wondering whether or not I 
>> reinvented the wheel.  Observe:
>>
>> t.test.sub <- function (formula, data, sub, ...)
>>     {
>>         for(i in 1:max(sub))
>>             {
>>                 print(t.test(formula, data = subset(data, sub == i), 
>> ...))
>>             }
>>     }
>>
>> Is there already a similar function in some package?
>>
>> Thanks,
>> Matthew Dubins
>>
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>