[R] Summary information by groups programming assitance

[William Revelle]

Yet another suggestion is describe.by in the psych package.

At 11:25 PM +0100 12/22/08, Søren Højsgaard wrote:
>Maybe summaryBy (or lapplyBy/splitBy) in the doBy package might help you.
>Regards
>Søren
>
>________________________________
>
>Fra: r-help-bounces at r-project.org på vegne af Ranney, Steven
>Sendt: ma 22-12-2008 22:51
>Til: r-help at r-project.org
>Emne: [R] Summary information by groups programming assitance
>
>
>
>All -
>
>I have data that looks like
>
>           psd   Species Lake Length  Weight    St.weight    Wr
>Wr.1     vol
>432  substock     SMB      Clear    150   41.00      0.01  95.12438
>95.10118  0.0105
>433  substock     SMB      Clear    152   39.00      0.01  86.72916
>86.70692  0.0105
>434  substock     SMB      Clear    152   40.00      3.11  88.95298
>82.03689  3.2655
>435  substock     SMB      Clear    159   48.00      0.04  92.42095
>92.34393  0.0420
>436  substock     SMB      Clear    159   48.00      0.01  92.42095
>92.40170  0.0105
>437  substock     SMB      Clear    165   47.00      0.03  80.38023
>80.32892  0.0315
>438  substock     SMB      Clear    171   62.00      0.21  94.58105
>94.26070  0.2205
>439  substock     SMB      Clear    178   70.00      0.01  93.91912
>93.90571  0.0105
>440  substock     SMB      Clear    179   76.00      1.38 100.15760
>98.33895  1.4490
>441       S-Q     SMB      Clear    180   75.00      0.01  97.09330
>97.08035  0.0105
>442       S-Q     SMB      Clear    180   92.00      0.02 119.10111
>119.07522  0.0210
>...
>[truncated]
>
>where psd and lake are categorical variables, with five and four
>categories, respectively.  I'd like to find the maximum vol and the
>lengths associated with each maximum vol by each category by each lake.
>In other words, I'd like to have a data frame that looks something like
>
>Lake            Category        Length  vol
>Clear           substock        152             3.2655
>Clear           S-Q             266             11.73
>Clear           Q-P             330             14.89
>...
>Pickerel        substock        170             3.4965
>Pickerel        S-Q             248             10.69
>Pickerel        Q-P             335             25.62
>Pickerel        P-M             415             32.62
>Pickerel        M-T             442             17.25 
>
>
>In order to originally get this, I used
>
>with(smb[Lake=="Clear",], tapply(vol, list(Length, psd),max))
>with(smb[Lake=="Enemy.Swim",], tapply(vol, list(Length, psd),max))
>with(smb[Lake=="Pickerel",], tapply(vol, list(Length, psd),max))
>with(smb[Lake=="Roy",], tapply(vol, list(Length, psd),max))
>
>and pulled the values I needed out by hand and put them into a .csv.
>Unfortunately, I've got a number of other data sets upon which I'll need
>to do the same analysis.  Finding a programmable alternative would
>provide a much easier (and likely less error prone) method to achieve
>the same results.  Ideally, the "Length" and "vol" data would be in a
>data frame such that I could then analyze with nls.
>
>Does anyone have any thoughts as to how I might accomplish this?
>
>Thanks in advance,
>
>Steven Ranney 
>
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>
>______________________________________________
>R-help at r-project.org mailing list
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>PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>and provide commented, minimal, self-contained, reproducible code.


-- 
William Revelle		http://personality-project.org/revelle.html
Professor			http://personality-project.org/personality.html
Department of Psychology             http://www.wcas.northwestern.edu/psych/
Northwestern University	http://www.northwestern.edu/
Attend  ISSID/ARP:2009               http://issid.org/issid.2009/