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.

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
)

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 23:00")
#> Warning: All formats failed to parse. No formats found.
head(data.1999)
#> # A tibble: 0 × 10
#> # ℹ 10 variables: date <dttm>, ws <dbl>, wd <int>, nox <int>, no2 <int>,
#> #   o3 <int>, pm10 <int>, so2 <dbl>, co <dbl>, pm25 <int>
tail(data.1999)
#> # A tibble: 0 × 10
#> # ℹ 10 variables: date <dttm>, ws <dbl>, wd <int>, nox <int>, no2 <int>,
#> #   o3 <int>, pm10 <int>, so2 <dbl>, co <dbl>, pm25 <int>

# or...
data.1999 <- selectByDate(mydata, start = "1999-01-01", end = "1999-12-31 23:00")
#> Warning: All formats failed to parse. No formats found.

# 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")
)


## 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"))