Yes!!  That did it!

Does .sub represent the different levels of the x$quiz indice?


jim holtman wrote:
> Is this what you were expecting?
>
>   
>> by(x, x$quiz, function(.sub) t.test(percent ~ group, data=.sub))
>>     
> x$quiz: 1
>
>         Welch Two Sample t-test
>
> data:  percent by group
> t = 6.3228, df = 6.231, p-value = 0.0006306
> alternative hypothesis: true difference in means is not equal to 0
> 95 percent confidence interval:
>  30.27235 67.94193
> sample estimates:
> mean in group High  mean in group Low
>           92.85714           43.75000
>
> ------------------------------------------------------------
> x$quiz: 2
>
>         Welch Two Sample t-test
>
> data:  percent by group
> t = 1.591, df = 5.875, p-value = 0.1638
> alternative hypothesis: true difference in means is not equal to 0
> 95 percent confidence interval:
>  -14.03856  65.46713
> sample estimates:
> mean in group High  mean in group Low
>           65.71429           40.00000
>
> ------------------------------------------------------------
> x$quiz: 3
>
>         Welch Two Sample t-test
>
> data:  percent by group
> t = -0.1541, df = 3.506, p-value = 0.886
> alternative hypothesis: true difference in means is not equal to 0
> 95 percent confidence interval:
>  -66.87207  60.20541
> sample estimates:
> mean in group High  mean in group Low
>           71.66667           75.00000
>
>   
>
>
> On 10/22/07, Matthew Dubins <matt.dubins@utoronto.ca> wrote:
>   
>> 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.
>>>>>>             
>>        [[alternative HTML version deleted]]
>>
>> ______________________________________________
>> 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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