[R] How to selectively sum rows [Beginner question]

[Aaron Siirila]

The count() function in the plyr package works beautifully. Thanks to Jim,
Rainer and Dennis for your help. 

Best.

-----Original Message-----
From: Dennis Murphy [mailto:djmuser at gmail.com] 
Sent: Monday, October 24, 2011 12:05 PM
To: asindc
Cc: r-help at r-project.org
Subject: Re: [R] How to selectively sum rows [Beginner question]

See the count() function in the plyr package; it does fast summation.
Something like

library('plyr')
count(passengerData, c('ORIGIN_WAC', 'DEST_WAC'), 'npassengers')

HTH,
Dennis

On Mon, Oct 24, 2011 at 8:27 AM, asindc <siirilaa at eastwestcenter.org> wrote:
> Hi, I am new to R so I would appreciate any help. I have some data that
has
> passenger flight data between city pairs. The way I got the data, there
are
> multiple rows of data for each city pair; the number of passengers needs
to
> be summed to get a TOTAL annual passenger count for each city pair.
>
> So my question is: how do I create a new table (or data frame) that
> selectively sums
>
> My initial thought would be to iterate through each row with the following
> logic:
>
> 1. If the ORIGIN_WAC and DEST_WAC pair are not in the new table, then add
> them to the table
> 2. If the ORIGIN_WAC and DEST_WAC pair already exist, then sum the
> passengers (and do not add a new row)
>
> Is this logical? If so, I think I just need some help on syntax (or do I
use
> a script?). Thanks.
>
> The first few rows of data look like this:
>
>
>
> --
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