[R] by Function Result Factor Levels

[David L Carlson]

Actually x is the variable name since your function returned a vector of three values: 

> tbl <- aggregate(warpbreaks[, 1], warpbreaks[, 2:3], function(breaks) c(Min = min(breaks),
+  Med = median(breaks), Max = max(breaks)))
> str(tbl)
'data.frame':   6 obs. of  3 variables:
 $ wool   : Factor w/ 2 levels "A","B": 1 2 1 2 1 2
 $ tension: Factor w/ 3 levels "L","M","H": 1 1 2 2 3 3
 $ x      : num [1:6, 1:3] 25 14 12 16 10 13 51 29 21 28 ...
  ..- attr(*, "dimnames")=List of 2
  .. ..$ : NULL
  .. ..$ : chr  "Min" "Med" "Max"

You have two options. One is to convert the matrix to three separate columns:

> tbl2 <- data.frame(tbl[, 1:2], tbl$x)
> str(tbl2)
'data.frame':   6 obs. of  5 variables:
 $ wool   : Factor w/ 2 levels "A","B": 1 2 1 2 1 2
 $ tension: Factor w/ 3 levels "L","M","H": 1 1 2 2 3 3
 $ Min    : num  25 14 12 16 10 13
 $ Med    : num  51 29 21 28 24 17
 $ Max    : num  70 44 36 42 43 28
> tbl2
  wool tension Min Med Max
1    A       L  25  51  70
2    B       L  14  29  44
3    A       M  12  21  36
4    B       M  16  28  42
5    A       H  10  24  43
6    B       H  13  17  28

The other is to change the name of x to something more informative:

> names(tbl)[3] <- "breaks"
> str(tbl)
'data.frame':   6 obs. of  3 variables:
 $ wool   : Factor w/ 2 levels "A","B": 1 2 1 2 1 2
 $ tension: Factor w/ 3 levels "L","M","H": 1 1 2 2 3 3
 $ breaks : num [1:6, 1:3] 25 14 12 16 10 13 51 29 21 28 ...
  ..- attr(*, "dimnames")=List of 2
  .. ..$ : NULL
  .. ..$ : chr  "Min" "Med" "Max"
> tbl
  wool tension breaks.Min breaks.Med breaks.Max
1    A       L         25         51         70
2    B       L         14         29         44
3    A       M         12         21         36
4    B       M         16         28         42
5    A       H         10         24         43
6    B       H         13         17         28

-------------------------------------
David L Carlson
Department of Anthropology
Texas A&M University
College Station, TX 77840-4352

-----Original Message-----
From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of Dario Strbenac
Sent: Wednesday, September 16, 2015 1:00 AM
To: William Dunlap
Cc: r-help at R-project.org
Subject: Re: [R] by Function Result Factor Levels

Good day,

Yes, exactly. I found that aggregate is another alternative which doesn't require a package dependency, although the column formatting is less suitable, always prepending x.

aggregate(warpbreaks[, 1], warpbreaks[, 2:3], function(breaks) c(Min = min(breaks), Med = median(breaks), Max = max(breaks)))
  wool tension x.Min x.Med x.Max
1    A       L    25    51    70
2    B       L    14    29    44
3    A       M    12    21    36
4    B       M    16    28    42
5    A       H    10    24    43
6    B       H    13    17    28

--------------------------------------
Dario Strbenac
PhD Student
University of Sydney
Camperdown NSW 2050
Australia
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