Hi,

Following please find *some* of my data.

percent 	quiz 	group
100 	1 	High
100 	1 	High
100 	1 	High
25 	1 	Low
50 	1 	Low
75 	1 	High
50 	1 	Low
75 	1 	High
100 	1 	High
100 	1 	High

50 	1 	Low
60 	2 	High
20 	2 	High
100 	2 	High
60 	2 	Low
40 	2 	Low
80 	2 	High
20 	2 	Low
60 	2 	High
40 	2 	High
100 	2 	High

90 	3 	High
100 	3 	High
0 	3 	High
90 	3 	Low
80 	3 	High
60 	3 	Low
100 	3 	High
60 	3 	High


Here is the by command i used:

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

Basically it gave me three of the same t.tests based on the full data 
set, not the subsets (quiz 1, 2 and 3).

So far it seems like my method is more straightforward!



Julian Burgos wrote:
> 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
>>>>
>>>> ______________________________________________
>>>> R-help@r-project.org mailing list
>>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>>> PLEASE do read the posting guide 
>>>> http://www.R-project.org/posting-guide.html
>>>> and provide commented, minimal, self-contained, reproducible code.
>>>
>>
>


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