[R] need more help.... Re: iterating over a data frame the R way?

[David Winsemius]

On Jan 1, 2010, at 11:20 AM, donahchoo at me.com wrote:

> Okay, I don't know if I'm blocking because of my other programming  
> language experience of if I'm just being dense.
>
> I have a data.frame with high,open,low,last,day, and start_time time  
> columns.  What I want to do is get all the rows with the same day  
> and process each of those columns.

The usual method of doing that sort of operation the application of a  
function within categories using tapply. See the examples in:

?tapply


> If I was able to run a query against the data.frame I would be want  
> something like:
>
> result = all the rows where the day is equal to 2007-12-05
>
> Then I would want get max(result["high"]), min(result["low"])
>
> How do I do this?  I tired sqldf, but its complaining about  
> libtcl0.5.8 not being found.  I'm on OS X 10.5.8 and haven't yet  
> tired to install a new version of tcl in /usr/local.
>
> Here's the dataframe:

Nope... nothing came through. Read the posting guide for the proper  
way to either include r objects in an email or to attache txt files.

David Winsemius, MD
Heritage Laboratories
West Hartford, CT