[R] apply

[Steven Yen]

Hello

I have a vector:

set.seed(123) > n<-3 > x<-rnorm(n); x [1] -0.56047565 -0.23017749 
1.55870831 I like to create a matrix with elements containing variances 
and covariances of x. That is var(x[1]) cov(x[1],x[2]) cov(x[1],x[3]) 
cov(x[2],x[1]) var(x[2]) cov(x[2],x[3]) cov(x[3],x[1]) cov(x[3],x[2]) 
var(x[3]) And I like to do it with "apply". Thanks.

On 10/4/2024 6:35 PM, Rui Barradas wrote:
> Hello,
>
> If you have a numeric matrix or data.frame, try something like
>
> cov(mtcars)
>
> Hope this helps,
>
> Rui Barradas
>
>
> Às 10:15 de 04/10/2024, Steven Yen escreveu:
>> On 10/4/2024 5:13 PM, Steven Yen wrote:
>>
>>> Pardon me!!!
>>>
>>> What makes you think this is a homework question? You are not
>>> obligated to respond if the question is not intelligent enough for you.
>>>
>>> I did the following: two ways to calculate a covariance matrix but
>>> wonder how I might replicate the results with "apply". I am not too
>>> comfortable with the online documentation of "apply".
>>>
>>>> set.seed(122345671) > n<-3 > x<-rnorm(n); x [1] 0.92098449 0.80940115
>>> 0.60374785 > cov1<-outer(x-mean(x),x-mean(x))/(n-1); cov1 [,1] [,2]
>>> [,3] [1,] 0.0102159207 0.00224105983 -0.0124569805 [2,] 0.0022410598
>>> 0.00049161983 -0.0027326797 [3,] -0.0124569805 -0.00273267965
>>> 0.0151896601 > cov2<-(x-mean(x))%*%t((x-mean(x)))/(n-1); cov2 [,1]
>>> [,2] [,3] [1,] 0.0102159207 0.00224105983 -0.0124569805 [2,]
>>> 0.0022410598 0.00049161983 -0.0027326797 [3,] -0.0124569805
>>> -0.00273267965 0.0151896601 >
>>> On 10/4/2024 4:57 PM, Uwe Ligges wrote:
>>>> Homework questions are not answered on this list.
>>>>
>>>> Best,
>>>> Uwe Ligges
>>>>
>>>>
>>>>
>>>> On 04.10.2024 10:32, Steven Yen wrote:
>>>>> The following line calculates standard deviations of a column vector:
>>>>>
>>>>> se<-apply(dd,1,sd)
>>>>>
>>>>> How can I calculate the covariance matrix using apply? Thanks.
>>>>>
>>>>> ______________________________________________
>>>>> R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
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>>>>> PLEASE do read the posting guide
>>>>> https://www.R-project.org/posting-guide.html
>>>>> and provide commented, minimal, self-contained, reproducible code.
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>>
>> ______________________________________________
>> R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide 
>> https://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>
>
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