selectByDate: Subset a data frame based on date

In davidcarslaw/openair: Tools for the Analysis of Air Pollution Data

Subset a data frame based on date

Description

Utility function to filter a data frame by a date range or specific date periods (month, year, etc.). All options are applied in turn, meaning this function can be used to select quite complex dates simply.

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 Date or POSIXct format.
start	A start date or date-time string in the form d/m/yyyy, m/d/yyyy, d/m/yyyy HH:MM, m/d/yyyy HH:MM, d/m/yyyy HH:MM:SS or m/d/yyyy HH:MM:SS.
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.

Author(s)

David Carslaw

Examples

## select all of 1999
data.1999 <- selectByDate(mydata, start = "1/1/1999", end = "31/12/1999 23:00")
head(data.1999)
tail(data.1999)

# or...
data.1999 <- selectByDate(mydata, start = "1999-01-01", end = "1999-12-31 23:00")

# 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")
)

davidcarslaw/openair documentation built on June 11, 2025, 10:27 p.m.