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

[Julian Burgos]

Could you post some of your data and your initial test, and explain why 
it didn't worked?  It is difficult to figure out what is the problem 
with your call to by().

Julian

Matthew Dubins wrote:
> 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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>>> and provide commented, minimal, self-contained, reproducible code.
>>
>