R help - Jan 2008 - Selecting rows conditionally between 2 data.frames

Hello everyone,

I have two data.frames that look like

calib:
place	zoom	scale
left		0.65		8
left		0.80		5.6
left		1.20		3
right		0.65		8.4
right		0.80		6
right		1.20		2.9

X:
...	place	zoom	....
...	left		0.80		....
...	left		1.20		....
...	right		0.65		....
...	NA		NA		....
...	right		0.8		....
...	left		1.20		....

and I want to get the corresponding values of 'scale' in a new column  
in X, i.e.:
X:
...	place	zoom	....	scale
...	left		0.80		....	5.6
...	left		1.20		....	3
...	right		0.65		....	8.4
...	NA		NA		....	NA
...	right		0.8		....	6
...	left		1.20		....	3

I tried various combination of `which` and `match` but could not make  
it work.
I fell back on defining a custom function and applying it over the lines
	get.scales <- function(x)
	{
		if (is.na(x$zoom)) {
			scaleF = NA
		} else {
			scaleF = calib[calib$zoom==x$zoom & calib$place==x$place,
"scale"]
		}
		return(scaleF)
	}
and
	apply(X, 1, get.scales)
but:
- this is not very practical since using apply apparently converts the  
data to an array and looses column titles (i.e. x$size does not work,  
I need to use column numbers, which I'd rather not)
- I feel there is an easier, vector based way.

I would welcome suggestions. Thank you in advance.

JiHO
---
http://jo.irisson.free.fr/

Looks like a job for

 	?merge

HTH,

Chuck


On Fri, 18 Jan 2008, jiho wrote:
> Hello everyone,
>
> I have two data.frames that look like
>
> calib:
> place	zoom	scale
> left		0.65		8
> left		0.80		5.6
> left		1.20		3
> right		0.65		8.4
> right		0.80		6
> right		1.20		2.9
>
> X:
> ...	place	zoom	....
> ...	left		0.80		....
> ...	left		1.20		....
> ...	right		0.65		....
> ...	NA		NA		....
> ...	right		0.8		....
> ...	left		1.20		....
>
> and I want to get the corresponding values of 'scale' in a new
column
> in X, i.e.:
> X:
> ...	place	zoom	....	scale
> ...	left		0.80		....	5.6
> ...	left		1.20		....	3
> ...	right		0.65		....	8.4
> ...	NA		NA		....	NA
> ...	right		0.8		....	6
> ...	left		1.20		....	3
>
> I tried various combination of `which` and `match` but could not make
> it work.
> I fell back on defining a custom function and applying it over the lines
> 	get.scales <- function(x)
> 	{
> 		if (is.na(x$zoom)) {
> 			scaleF = NA
> 		} else {
> 			scaleF = calib[calib$zoom==x$zoom & calib$place==x$place,
"scale"]
> 		}
> 		return(scaleF)
> 	}
> and
> 	apply(X, 1, get.scales)
> but:
> - this is not very practical since using apply apparently converts the
> data to an array and looses column titles (i.e. x$size does not work,
> I need to use column numbers, which I'd rather not)
> - I feel there is an easier, vector based way.
>
> I would welcome suggestions. Thank you in advance.
>
> JiHO
> ---
> http://jo.irisson.free.fr/
>
> ______________________________________________
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> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
Charles C. Berry                            (858) 534-2098
                                             Dept of Family/Preventive Medicine
E mailto:cberry at tajo.ucsd.edu	            UC San Diego
http://famprevmed.ucsd.edu/faculty/cberry/  La Jolla, San Diego 92093-0901