[R] Finding values in a dataframe at a specified hour

[PIKAL Petr]

Hi

I presume your data frames are not big. What about merging them by hour and comparing appropriate columns?

something like

windMerged<-merge(windHW, spring, by = "hour", all=TRUE)
sel <- which(windMerged[, xx] >= windMerged[,yy])
windMerged[sel, xx] <- NA

Untested because lack of data.

Cheers
Petr

> -----Original Message-----
> From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of
> Alexandra Catena
> Sent: Friday, April 10, 2015 11:07 PM
> To: r-help at r-project.org
> Subject: Re: [R] Finding values in a dataframe at a specified hour
>
> Update:
>
> I have this so far.  * The first column of windHW is the wind speed.
> The 5th column of the dataframe, spring, is the 5*sigma value of every
> hour.  hourRow gives out all the rows of wind speed at a given hour.
>
> for (i in 0:23){
>   hourRow = which(windHW$hour==i,arr.ind=TRUE)
>   for (h in hourRow){
>     if (windHW[h,1]>=spring[spring$hour==i,5]){
>       windHW[h,1]<-NA}
>   }
> }
>
> This then gives the error: Error in if (windHW[h, 1] >=
> spring[spring$hour == i, 5]) { : argument is of length zero
>
> *Note: The dataframe for each of the seasons have 24 rows corresponding
> to each hour of the day 0:23.
>
> Thanks,
> Alexandra
>
>
> On Fri, Apr 10, 2015 at 1:07 PM, Alexandra Catena <amc5981 at gmail.com>
> wrote:
> > Hello,
> >
> > I have a large dataframe (windHW) of wind speeds (ws) at each hour
> > from many days over a set of years.  Some of these values are
> > obviously wrong (600 m/s) and I want to get rid of all the values
> that
> > are larger than 5*sigma for each hour.  The 5*sigma (variable name
> > sigma5) values are located in different dataframes for each season,
> > with each dataframe titled as a season.  For example, in the
> > dataframe, spring, the 5*sigma value is 79.6 m/s for hour 1.
> >
> > So my question is as follows: how can I get it so that the code will
> > be able to find all the wind speed values in the dataframe, windHW,
> of
> > a specific hour be higher than the 5*sigma value at that hour?
> > For example, I would like to find if any of the wind speed values at
> > hour 1 are higher than 79.6 m/s, and if so, then replace that value
> > with NA.
> >
> > I have something like this but I can't seem to figure out how to get
> > it for specific hours:
> >
> > windHW$ws[windHW$ws>=spring$sigma5] <- NA
> >
> > I imported the data using readLines and into the dataframe windHW.  I
> > also have R version 3.1.1
> >
> > Any help would be appreciated!
> >
> > Thanks,
> > Alexandra
>
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> and provide commented, minimal, self-contained, reproducible code.

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