# [R] correlation with boot

Prof Brian Ripley ripley at stats.ox.ac.uk
Tue Sep 2 09:26:33 CEST 2008

```On Tue, 2 Sep 2008, ctu at bigred.unl.edu wrote:

> Hi Professor Ripley,
> (Thank you very much)^infinite for your response. I still have few questions
> 1. R shows that I have two column in nlaw data.
>> ncol(nlaw)
> [1] 2
>> corr(nlaw)
> [1] 0.7763745

Since we don't have law, we don't know what nlaw is: you recomputed it
after listing it.

> 2. Why can't I use boot::corr? I check corr in boot package and it seems to
> be used for computing correlation coefficient,right?

You can, but you need to use it correctly.  I gave you one suggestion that
most people find simpler to understand.

> 3. The last question, cor is for computed the correlation variance and
> covariance matrix. Would you give a explanation for  cor(data[ind,])[1,2]
> I do not get it.

Try the pieces for yourself.  What does cor(nlaw) give? cor(nlaw)[1,2]?

>
> Appreciate,
> Chunhao
>
>
> Quoting Prof Brian Ripley <ripley at stats.ox.ac.uk>:
>
>> Please look at the help for boot, in particular what it says the form
>> of 'statistic' should be.  Possibly what you want is
>>
>> corr.t <- function(data, ind) cor(data[ind,])[1,2]
>>
>> nlaw appears to be a single-column matrix: that will not work either.
>>
>> On Mon, 1 Sep 2008, ctu at bigred.unl.edu wrote:
>>
>>> Hi R users,
>>> I have one simple question but I really don't know why I can't get it
>>> work.
>>> The data was adopted from Efron's An introduction to the bootstrap book.
>>>> nlaw
>>>   LSAT  GPA
>>> [1,]  576 3.39
>>> [2,]  635 3.30
>>> [3,]  558 2.81
>>> [4,]  578 3.03
>>> [5,]  666 3.44
>>> [6,]  580 3.07
>>> [7,]  555 3.00
>>> [8,]  661 3.43
>>> [9,]  651 3.36
>>> [10,]  605 3.13
>>> [11,]  653 3.12
>>> [12,]  575 2.74
>>> [13,]  545 2.76
>>> [14,]  572 2.88
>>> [15,]  594 2.96
>>>> nlaw<-as.matrix(law[,-1])
>>>> corr.t<-function(data){
>>> +        return(boot::corr(data))
>>> +        }
>>>> law.boot<-boot(data=nlaw,statistic=corr.t,R=49)
>>> Error in statistic(data, original, ...) : unused argument(s) (1:15)
>>>
>>> many thanks for the help
>>> Chunhao
>>>
>>> ______________________________________________
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>>> and provide commented, minimal, self-contained, reproducible code.
>>
>> --
>> Brian D. Ripley,                  ripley at stats.ox.ac.uk
>> Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
>> University of Oxford,             Tel:  +44 1865 272861 (self)
>> 1 South Parks Road,                     +44 1865 272866 (PA)
>> Oxford OX1 3TG, UK                Fax:  +44 1865 272595
>
>
>

--
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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