[R] newbie question: grouping rows

Christos Hatzis christos at silicoinsights.com
Sat Mar 11 06:00:28 CET 2006

As Thomas suggested the solution is in the R-FAQ which is worth reading

as.numeric(as.character(old$q.D1)) < 0.05

If you try the above without the 'as.character()' you will see why this is


-----Original Message-----
From: Matthew Scholz [mailto:schmatthew at gmail.com] 
Sent: Friday, March 10, 2006 7:41 PM
To: christos at silicoinsights.com
Cc: r-help at stat.math.ethz.ch
Subject: Re: [R] newbie question: grouping rows

Thanks for your response, Christos, but when I try this:

> new = old[old$q.D1 < 0.05,]

I get the following warning (and what I'm trying to do fails):

Warning message:
< not meaningful for factors in: Ops.factor(old$q.D1, 0.05)

I've tried to bone up on the topic of factors and searching R help, but I'm
still not sure why my data is being converted to that class nor do I know
how to undo the conversion or work around it. Thanks again in advance of
your advice. Any suggestions?


On 3/9/06, Christos Hatzis <christos at silicoinsights.com> wrote:
> You can try:
> new.dataframe <- my.dataframe[my.dataframe$p.value < 0.05, ]
> This will select all columns.  Alternatively, you can specify the 
> columns that you want after the ",".
> -Christos
> -----Original Message-----
> From: r-help-bounces at stat.math.ethz.ch 
> [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Matthew Scholz
> Sent: Thursday, March 09, 2006 5:18 PM
> To: r-help at stat.math.ethz.ch
> Subject: [R] newbie question: grouping rows
> Hi all,
> I have a very simple question that I can't seem to find the answer to.
> How do I extract rows that meet a certain criteria  from a data frame 
> and group them into a new data frame? For example, if I want to make a 
> new data frame that only includes rows of data for which the p values 
> (given by one of the columns in the data frame) are less than a 
> certain value, how do I do this? It seems that there should be a 
> simple function that does this. I looked into getGroups from the nmle 
> package, but am not sure how to construct the form argument correctly 
> or even if it's the appropriate way to tackle this.
> Thanks in advance of your answer,
> Matt
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