[R] detecting measurement of specific id in column in R

[Romy Rehschuh]

Dear all,

if the attachment didn´t arrive, maybe it works now.
I would like to substract the "IN" values (= the air which goes into the
chambers) for "d13C", "ppm_CO2" and "ppm_13CO2"
from the "d13C", "ppm_CO2" and "ppm_13CO2" for every single chamber.
I need to substract the "IN" values which were measured *before* the
chamber.

So the calculation would look like df$d13C [chambers] - df$d13C [IN]
                                                       df$ppm_CO2
[chambers] - df$ppm_13CO2 [IN]
                                                       df$ppm_13CO2
[chambers] - df$ ppm_13CO2 [IN]
--> for chamber 101-111 this should be the first "IN" (No 1)
--> for chamber 1-11 this should be the second "IN" (No 12)
...and so on

I tried sth. like which(abs(date-x) == min(abs(date-x), but it just gives
me the closest "IN" in time and not the "IN" before.

I would appreciate any help!
Thank you so much, Vicci

Am Do., 22. Nov. 2018 um 17:53 Uhr schrieb Rui Barradas <
ruipbarradas using sapo.pt>:

> Hello,
>
> No attachment arrived.
> R-help allows only a limited number of file types to be attached, if you
> file is a text file, change its extension to .txt an try again, please.
>
> Hope this helps,
>
> Rui Barradas
>
> Às 09:33 de 22/11/2018, Romy Rehschuh via R-help escreveu:
> > Dear all,
> >
> > I hope this is the right way to ask questions.
> > I have a problem with R regarding the detection of the measurement of a
> > specific sample_id (see example file attached). I have to substract the
> > "IN" values (means the air which goes into the chambers) from the values
> of
> > "d13C", "ppm_CO2" and "ppm_13CO2" for every single chamber (=sample ID).
> > The "IN" values have to be the ones which were measured* before *the
> > measurements of the single chambers in time. I measured "IN" once and
> then
> > up to 10 chambers in a row to safe time, then "IN" again, but it can
> change.
> > Therefore, searching for the closest "IN" does not work.
> >
> > Do you have any suggestions? Would it be possible to write a loop for
> this?
> > I would really much appreciate your help!
> >
> > Best, Vicci
> > ______________________________________________
> > R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> > and provide commented, minimal, self-contained, reproducible code.
> >
>

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