[R] How to get row index of sorted matrix

[Gundala Viswanath]

Thanks Jim. That's does exactly what I am looking for.

- Gundala Viswanath
Jakarta - Indonesia


On Tue, Jun 24, 2008 at 11:13 AM, jim holtman <jholtman at gmail.com> wrote:
> Is this what you were looking for:
>
>> x <- scan(textConnection(" 1372.23718 2.277450e+04
> +    74.48333 5.494448e+01
> +   226.63590 6.023199e+02
> +  1947.17564 4.044391e+04
> +   178.79615 3.970006e+02
> +   657.56857 3.396852e+04
> +   251.60519 1.239538e+03
> +    78.53846 7.473607e+01
> +   140.37564 2.395830e+02
> +    358.13718 1.508718e+03"), what=0)
> Read 20 items
>> closeAllConnections()
>> mydata <- matrix(x, ncol=2, byrow=TRUE)
>> mydata
>            [,1]        [,2]
>  [1,] 1372.23718 22774.50000
>  [2,]   74.48333    54.94448
>  [3,]  226.63590   602.31990
>  [4,] 1947.17564 40443.91000
>  [5,]  178.79615   397.00060
>  [6,]  657.56857 33968.52000
>  [7,]  251.60519  1239.53800
>  [8,]   78.53846    74.73607
>  [9,]  140.37564   239.58300
> [10,]  358.13718  1508.71800
>> # top 3 indices
>> order(mydata[,2], decreasing=TRUE)[1:3]
> [1] 4 6 1
>> # print out the ordered data
>> mydata[order(mydata[,2], decreasing=TRUE),]
>            [,1]        [,2]
>  [1,] 1947.17564 40443.91000
>  [2,]  657.56857 33968.52000
>  [3,] 1372.23718 22774.50000
>  [4,]  358.13718  1508.71800
>  [5,]  251.60519  1239.53800
>  [6,]  226.63590   602.31990
>  [7,]  178.79615   397.00060
>  [8,]  140.37564   239.58300
>  [9,]   78.53846    74.73607
> [10,]   74.48333    54.94448
>>
>
>
> On Mon, Jun 23, 2008 at 9:35 PM, Gundala Viswanath <gundalav at gmail.com> wrote:
>> Hi,
>>
>> How can I get the top-3 index (sorted by "var") of the following
>> matrix?
>>
>>> print(mydata)
>>                                 var
>>  [1,]  1372.23718 2.277450e+04
>>  [2,]    74.48333 5.494448e+01
>>  [3,]   226.63590 6.023199e+02
>>  [4,]  1947.17564 4.044391e+04
>>  [5,]   178.79615 3.970006e+02
>>  [6,]   657.56857 3.396852e+04
>>  [7,]   251.60519 1.239538e+03
>>  [8,]    78.53846 7.473607e+01
>>  [9,]   140.37564 2.395830e+02
>>  [10,]   358.13718 1.508718e+03
>>
>>
>> - Gundala Viswanath
>> Jakarta - Indonesia
>>
>> ______________________________________________
>> R-help at 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.
>>
>
>
>
> --
> Jim Holtman
> Cincinnati, OH
> +1 513 646 9390
>
> What is the problem you are trying to solve?
>