Function to extract run lengths greater than a threshold
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")
)mydata |
A data frame with a |
pollutant |
Name of variable to process. Mandatory. |
criterion |
Condition to select run lengths e.g. |
run.len |
Run length for extracting contiguous values of
|
threshold |
The threshold value for |
result |
A new column |
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
concentrations.
Returns a data frame that meets the chosen criteria. See examples below.
David Carslaw
## 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 ## Not run: polarPlot(mydata, pollutant = "nox", type = "criterion")
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