[R] Conditional statement used in sapply()

[Steven McKinney]

> -----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 3:03 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
> + })
> 

You probably want something such as
result<-sapply(res, function(.df) {  mean(.df$Volume[.df$Volume>0]) })  

HTH
Steve McKinney

> 
> 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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