[R] Selecting rows conditionally between 2 data.frames
Charles C. Berry
cberry at tajo.ucsd.edu
Fri Jan 18 20:13:13 CET 2008
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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> 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
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