[R] counting subgroup sums within a data frame

[ONKELINX, Thierry]

Have a look at the reshape package.

Assuming that your data is in a data.frame called "dataset".

cast(Date ~ ., data = dataset, value = "count", fun = sum) 
cast(Date ~ class, data = dataset, value = "count", fun = sum) 
cast(Date + class ~ ., data = dataset, value = "count", fun = sum) 

Or the plyr package

ddply(dataset, c("Date"), function(x){c(Sum_of_counts = sum(x$count))})
ddply(dataset, c("Date", "class"), function(x){c(Sum_of_counts =
sum(x$count))})

HTH,

Thierry

------------------------------------------------------------------------
----
ir. Thierry Onkelinx
Instituut voor natuur- en bosonderzoek / Research Institute for Nature
and Forest
Cel biometrie, methodologie en kwaliteitszorg / Section biometrics,
methodology and quality assurance
Gaverstraat 4
9500 Geraardsbergen
Belgium
tel. + 32 54/436 185
Thierry.Onkelinx at inbo.be
www.inbo.be

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than asking him to perform a post-mortem examination: he may be able to
say what the experiment died of.
~ Sir Ronald Aylmer Fisher

The plural of anecdote is not data.
~ Roger Brinner

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ensure that a reasonable answer can be extracted from a given body of
data.
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-----Oorspronkelijk bericht-----
Van: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
Namens Shaun Grannis
Verzonden: woensdag 26 augustus 2009 15:07
Aan: r-help at r-project.org
Onderwerp: [R] counting subgroup sums within a data frame

Hi,

I'm sure there's an easy approach to this issue, I'm just not seeing it.

I have a data frame of the following form:

  Date     class    subclass   count
8/1/2009    A        X          1
8/1/2009    B        X          2
8/1/2009    A        Y          9
8/1/2009    B        Y          3
8/2/2009    A        X          1
8/2/2009    B        X          5
8/2/2009    A        Y          4
8/2/2009    B        Y          2
8/3/2009    A        X          6
8/3/2009    B        X          4
8/3/2009    A        Y          3
8/3/2009    B        Y          4
8/4/2009    A        X          1
8/4/2009    B        X          9
8/4/2009    A        Y          3
8/4/2009    B        Y          5
8/5/2009    A        X          3
8/5/2009    B        X          7
8/5/2009    A        Y          2
8/5/2009    B        Y          1

I would like to create a data frame of the sum the daily counts for,
say, class 'A', like so:


  Date     sum_of_counts
8/1/2009       10
8/2/2009        5
8/3/2009        9
8/4/2009        4
8/5/2009        5

I ultimately would like to do sum of counts on all classes and
subclasses.  It seems that this is equivalent to a GROUP BY query in
SQL.

I'm sure this is possible in R. Any suggestions?

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