[R] Using "apply" instead of "for" loop / multithreading

[jim holtman]

Since you did not provide sample data (use dput instead of posting
links to 'jpg' files), you can probably do it without loops:

k=resp[,5]
CO2umol <- resp[,6]*((Press*infoch[k,11]*1e-6)/(R*(resp[,7]+273.15)))
CO2v <- CO2umol/(infoch[k,10])
CO2s <- CO2umol/(infoch[k,9]

On Mon, Nov 12, 2012 at 12:39 PM, Charles D. <charlybegood at live.fr> wrote:
> Hello ,
>
> I'm new to R and don't really understand how to use the function "apply"
> instead of a "for loop", particularly for a function with multiple entries.
> I have a big data file and would like to apply a function in multi thread to
> accelerate the processus.
>
> I have a data frame containing values of* CO2 in ppm (resp[i,6])* that I
> want to convert in umol of CO2 emitted by stem volume biomass (CO2v) and
> stem area (CO2s). (tree respiration)
>
> The loop that I have is calculating the CO2 fluxes for each row.
>
> *Script :*
> for (i in 1:nrow(resp)) {
> k=resp[i,5]
> CO2umol[i]<-resp[i,6]*((Press*infoch[k,11]*1e-6)/(R*(resp[i,7]+273.15)))
> CO2v[i]<-CO2umol[i]/(infoch[k,10])
> CO2s[i]<-CO2umol[i]/(infoch[k,9])
> }
>
> For that, I have two data frames :
> - *infoch :* variables used to calculate CO2 fluxes (16 rows with the
> characteristics of 16 analysis chambers)
>
> <http://r.789695.n4.nabble.com/file/n4649326/infoch.jpg>
>
> - *resp: *time series containing CO2 values and temperatures by chamber
> analysed (more than 500.000 rows)
>
> <http://r.789695.n4.nabble.com/file/n4649326/resp.jpg>
>
> other variables :
> Press=93000
> R=8.31
>
> The loop is working good, but taking quite a long time to process, if
> someone could explain me how to use the apply function in this case, it
> would be really helpful.
>
> Thanks
> Charles
>
>
>
> --
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>
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-- 
Jim Holtman
Data Munger Guru

What is the problem that you are trying to solve?
Tell me what you want to do, not how you want to do it.