Subset a data frame based on date — selectByDate • openair

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

David Carslaw

Examples


## select all of 1999
data.1999 <- selectByDate(mydata, start = "1/1/1999", end = "31/12/1999 23:00")
head(data.1999)
#> # A tibble: 6 × 10
#>   date                   ws    wd   nox   no2    o3  pm10   so2    co  pm25
#>   <dttm>              <dbl> <int> <int> <int> <int> <int> <dbl> <dbl> <int>
#> 1 1999-01-01 00:00:00  5.04   140    88    35     4    21  3.84 1.02     18
#> 2 1999-01-01 01:00:00  4.08   160   132    41     3    17  5.24 2.7      11
#> 3 1999-01-01 02:00:00  4.8    160   168    40     4    17  6.51 2.87      8
#> 4 1999-01-01 03:00:00  4.92   150    85    36     3    15  4.18 1.62     10
#> 5 1999-01-01 04:00:00  4.68   150    93    37     3    16  4.25 1.02     11
#> 6 1999-01-01 05:00:00  3.96   160    74    29     5    14  3.88 0.725    NA
tail(data.1999)
#> # A tibble: 6 × 10
#>   date                   ws    wd   nox   no2    o3  pm10   so2    co  pm25
#>   <dttm>              <dbl> <int> <int> <int> <int> <int> <dbl> <dbl> <int>
#> 1 1999-12-31 18:00:00  4.68   190   226    39    NA    29  5.46  2.38    23
#> 2 1999-12-31 19:00:00  3.96   180   202    37    NA    27  4.78  2.15    23
#> 3 1999-12-31 20:00:00  3.36   190   246    44    NA    30  5.88  2.45    23
#> 4 1999-12-31 21:00:00  3.72   220   231    35    NA    28  5.28  2.22    23
#> 5 1999-12-31 22:00:00  4.08   200   217    41    NA    31  4.79  2.17    26
#> 6 1999-12-31 23:00:00  3.24   200   181    37    NA    28  3.48  1.78    22

# 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")
)