Subset a data frame based on date — selectByDate • openair

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

David Carslaw

Examples


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

# 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"))