selectByDate: Subset a data frame based on date

In openair: Tools for the Analysis of Air Pollution Data

Subset a data frame based on date

Description

Utility function to make it easier to select periods from a data frame before sending to a function

Usage

selectByDate(
  mydata,
  start = "1/1/2008",
  end = "31/12/2008",
  year = 2008,
  month = 1,
  day = "weekday",
  hour = 1
)

Arguments

mydata	A data frame containing a date field in hourly or high resolution format.
start	A start date string in the form d/m/yyyy e.g. “1/2/1999” or in ‘R’ format i.e. “YYYY-mm-dd”, “1999-02-01”
end	See start for format.
year	A year or years to select e.g. year = 1998:2004 to select 1998-2004 inclusive or year = c(1998, 2004) to select 1998 and 2004.
month	A month or months to select. Can either be numeric e.g. month = 1:6 to select months 1-6 (January to June), or by name e.g. month = c("January", "December"). Names can be abbreviated to 3 letters and be in lower or upper case.
day	A day name or or days to select. day can be numeric (1 to 31) or character. For example day = c("Monday", "Wednesday") or day = 1:10 (to select the 1st to 10th of each month). Names can be abbreviated to 3 letters and be in lower or upper case. Also accepts “weekday” (Monday - Friday) and “weekend” for convenience.
hour	An hour or hours to select from 0-23 e.g. hour = 0:12 to select hours 0 to 12 inclusive.

Details

This function makes it much easier to select periods of interest from a data frame based on dates in a British format. Selecting date/times in R format can be intimidating for new users. This function can be used to select quite complex dates simply - see examples below.

Dates are assumed to be inclusive, so start = "1/1/1999" means that times are selected from hour zero. Similarly, end = "31/12/1999" will include all hours of the 31st December. start and end can also be in standard R format as a string i.e. "YYYY-mm-dd", so start = "1999-01-01" is fine.

All options are applied in turn making it possible to select quite complex dates

Author(s)

David Carslaw

Examples

## select all of 1999
data.1999 <- selectByDate(mydata, start = "1/1/1999", end = "31/12/1999")
head(data.1999)
tail(data.1999)

# or...
data.1999 <- selectByDate(mydata, start = "1999-01-01", end = "1999-12-31")

# easier way
data.1999 <- selectByDate(mydata, year = 1999)


# more complex use: select weekdays between the hours of 7 am to 7 pm
sub.data <- selectByDate(mydata, day = "weekday", hour = 7:19)

# select weekends between the hours of 7 am to 7 pm in winter (Dec, Jan, Feb)
sub.data <- selectByDate(mydata, day = "weekend", hour = 7:19, month =
c("dec", "jan", "feb"))

openair documentation built on May 29, 2024, 11:07 a.m.