[R] Conditional statement used in sapply()

[Ling, Gary (Electronic Trading)]

Hi Mark, 

How about this?

result <- sapply(split(res, res$Volume>0)$`TRUE`, mean)

There is one thing I'm not sure: is res$Volume a vector or single
numeric?

-gary

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On Behalf Of Altaweel, Mark R.
Sent: Wednesday, August 13, 2008 6:03 PM
To: r-help at r-project.org
Subject: [R] Conditional statement used in sapply()


Hi,

I have data stored in a list that I would like to aggregate and perform
some basic stats. However, I would like to apply conditional statements
so that not all the data are used.  Basically, I want to get a specific
variable, do some basic functions (such as a mean), but only get the
data in each element's data that match the condition. The code I used is
below:

> result<-sapply(res, function(.df) {   #res is the list containing file
data
+ if(.df$Volume>0)mean(.df$Volume)  #only have the mean function
calculate on values great than 0
+ })


I did get a numeric output; however, when I checked the output value the
conditional was ignored (i.e. it did not do anything to the calculation)

I also obtained these warning statements:

Warning messages:
1: In if (.df$Volume > 0) mean(.df$Volume) :
  the condition has length > 1 and only the first element will be used
2: In if (.df$Volume > 0) mean(.df$Volume) :
  the condition has length > 1 and only the first element will be used

Please let me know what am I doing wrong and how can I apply a
conditional statement to the sapply function.

Thanks

Mark

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