[R] splitting data frame based on a criteria

Ingmar Visser i.visser at uva.nl
Tue Jun 3 21:11:29 CEST 2008

?by may be helpful here
eg if dat is your data.frame and yf is a factor (created using ifelse)
use by(dat,yf,mean) to compute the means for each level of yf
hth, Ingmar

On Jun 3, 2008, at 8:37 PM, Marvin Lists wrote:

> Hi,
> I have a data frame that I want to split into two based on the  
> values of a
> variable in it.
> The variable Y has numeric values ranging between 0 through 70. I  
> want to
> plot the frequencies of another variable X in two different cases:
> - When Y = 0 and
> - When Y > 0
> How does one go about doing this?
> In general, I want to do several analyses with this data frame that  
> are a
> variation of the above situation, i.e. they require splitting the  
> data into
> different age, gender etc. and then calculating separate means,  
> correlations
> and so on for the different groups into which the data frame would  
> split.
> I am struggling with the correct syntax for achieving this.
> Reading through the documentation suggests that tapply and split  
> may be the
> functions to use for my purposes but the examples in the  
> documentations
> didn't help me understand how I could achieve this.
> I would appreciate any suggestions and help.
> Thanks,
> Marvin
> 	[[alternative HTML version deleted]]
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