Function to extract run lengths greater than a thresholdSource:
Utility function to extract user-defined run lengths (durations) above a threshold
selectRunning( mydata, pollutant = "nox", criterion = ">", run.len = 5, threshold = 500, result = c("yes", "no") )
A data frame with a
datefield and at least one numeric
pollutantfield to analyse.
Name of variable to process. Mandatory.
Condition to select run lengths e.g.
">"with select data more than
Run length for extracting contiguous values of
The threshold value for
pollutantabove which data should be extracted.
A new column
criterionis returned with string to identity whether condition was met.
This is a utility function to extract runs of values above a certain threshold. For example, for a data frame of hourly NOx values we would like to extract all those hours where the concentration is at least 500ppb for contiguous periods of 5 or more hours.
This function is useful, for example, for selecting pollution episodes from
a data frame i.e. where concentrations remain elevated for a certain period
of time. It may also be of more general use when analysing air pollution
data. For example,
selectRunning could be used to extract continuous
periods of rainfall --- which could be important for particle
## extract those hours where there are at least 5 consecutive NOx ## concentrations above 500ppb mydata <- selectRunning(mydata, run.len = 5, threshold = 500) ## make a polar plot of those conditions...shows that those ## conditions are dominated by low wind speeds, not ## in-canyon recirculation if (FALSE) polarPlot(mydata, pollutant = "nox", type = "criterion")