Re: [R] How to get row index of sorted matrix

From: Gundala Viswanath <gundalav_at_gmail.com>
Date: Tue, 24 Jun 2008 11:20:33 +0900

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

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?
>



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