Summary using by() returns character arrays in a list

Hi

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
project.org] On Behalf Of Alex van der Spek
Sent: Wednesday, October 10, 2012 2:48 PM
To: r-help at r-project.org
Subject: [R] Summary using by() returns character arrays in a list

I use by() to generate a summary statistics like so:

Lbys <- by(dat[Nidx], dat$LipTest, summary)

where Nidx is an index vector with names picking out the columns in the
data frame dat.

This returns a list of character arrays (see below for str() output)
where the columns are named correctly but the rownames are empty
strings and the values are strings prepended with the summary
statistic's name (e.g.
"Min.", "Median ").

Without knowledge of your data it is difficult to understand what is
wrong.

If I use iris data set as input everything goes as expected
data(iris)

summary(iris)

  Sepal.Length    Sepal.Width     Petal.Length    Petal.Width
 Min.   :4.300   Min.   :2.000   Min.   :1.000   Min.   :0.100
 1st Qu.:5.100   1st Qu.:2.800   1st Qu.:1.600   1st Qu.:0.300
 Median :5.800   Median :3.000   Median :4.350   Median :1.300
 Mean   :5.843   Mean   :3.057   Mean   :3.758   Mean   :1.199
 3rd Qu.:6.400   3rd Qu.:3.300   3rd Qu.:5.100   3rd Qu.:1.800
 Max.   :7.900   Max.   :4.400   Max.   :6.900   Max.   :2.500
       Species
 setosa    :50
 versicolor:50
 virginica :50

by(iris, iris$Species, summary)

iris$Species: setosa
  Sepal.Length    Sepal.Width     Petal.Length    Petal.Width
 Min.   :4.300   Min.   :2.300   Min.   :1.000   Min.   :0.100
 1st Qu.:4.800   1st Qu.:3.200   1st Qu.:1.400   1st Qu.:0.200
 Median :5.000   Median :3.400   Median :1.500   Median :0.200
 Mean   :5.006   Mean   :3.428   Mean   :1.462   Mean   :0.246
 3rd Qu.:5.200   3rd Qu.:3.675   3rd Qu.:1.575   3rd Qu.:0.300
 Max.   :5.800   Max.   :4.400   Max.   :1.900   Max.   :0.600
       Species
 setosa    :50
 versicolor: 0
 virginica : 0

I am reading the code of summary.data.frame() but can't figure out how
I can change the action of that function to return list of numeric
matrices with as rownames the summary statistic's name ("Min.", "Max."
etc) and as values the numeric values of the calculated summary
statistic.

Just what do you not like on such output and how do you want the output
structured?
Maybe you want aggregate, but without simple data it is hard to say.

aggregate(iris[1:2], list(iris$Species), summary)

Regards
Petr

Any help much appreciated!
Regards,
Alex van der Spek

str(Lbys)

List of 2
 $    : 'table' chr [1:6, 1:19] "Min.   :-0.190  " "1st Qu.: 9.297  "
"Median :10.373  " "Mean   :10.100  " ...
  ..- attr(*, "dimnames")=List of 2
  .. ..$ : chr [1:6] "" "" "" "" ...
  .. ..$ : chr [1:19] "Cell_3_SOS....GVF." "Cell_3_SOSq..ms.ms."
"Cell_3_Airflow..cfm." "Cell_3_Float..in.." ...
 $ T38: 'table' chr [1:6, 1:19] "Min.   :8.648  " "1st Qu.:8.920  "
"Median :9.018  " "Mean   :9.027  " ...
  ..- attr(*, "dimnames")=List of 2
  .. ..$ : chr [1:6] "" "" "" "" ...
  .. ..$ : chr [1:19] "Cell_3_SOS....GVF." "Cell_3_SOSq..ms.ms."
"Cell_3_Airflow..cfm." "Cell_3_Float..in.." ...
 - attr(*, "dim")= int 2
 - attr(*, "dimnames")=List of 1
  ..$ dat$LipTest: chr [1:2] "" "T38"
 - attr(*, "call")= language by.data.frame(data = dat[Nidx], INDICES =
dat$LipTest, FUN = summary)
 - attr(*, "class")= chr "by"