selectRunning {openair} | R Documentation |
Function to extract run lengths greater than a threshold
Description
Utility function to extract user-defined run lengths (durations) above a threshold
Usage
selectRunning(
mydata,
pollutant = "nox",
criterion = ">",
run.len = 5,
threshold = 500,
result = c("yes", "no")
)
Arguments
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 |
Details
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.
Value
Returns a data frame that meets the chosen criteria. See examples below.
Author(s)
David Carslaw
Examples
## 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")