Calculate monthly summary statistics — calc_monthly

Calculates means, medians, maximums, minimums, and percentiles for each month of all years of flow values from a daily streamflow data set. Calculates statistics from all values, unless specified. Returns a tibble with statistics.

calc_monthly_stats(
  data,
  dates = Date,
  values = Value,
  groups = STATION_NUMBER,
  station_number,
  percentiles = c(10, 90),
  roll_days = 1,
  roll_align = "right",
  water_year_start = 1,
  start_year,
  end_year,
  exclude_years,
  months = 1:12,
  transpose = FALSE,
  spread = FALSE,
  ignore_missing = FALSE
)

Arguments

data	Data frame of daily data that contains columns of dates, flow values, and (optional) groups (e.g. station numbers). Leave blank if using `station_number` argument.
dates	Name of column in `data` that contains dates formatted YYYY-MM-DD. Only required if dates column name is not 'Date' (default). Leave blank if using `station_number` argument.
values	Name of column in `data` that contains numeric flow values, in units of cubic metres per second. Only required if values column name is not 'Value' (default). Leave blank if using `station_number` argument.
groups	Name of column in `data` that contains unique identifiers for different data sets, if applicable. Only required if groups column name is not 'STATION_NUMBER'. Function will automatically group by a column named 'STATION_NUMBER' if present. Remove the 'STATION_NUMBER' column beforehand to remove this grouping. Leave blank if using `station_number` argument.
station_number	Character string vector of seven digit Water Survey of Canada station numbers (e.g. `"08NM116"`) of which to extract daily streamflow data from a HYDAT database. Requires `tidyhydat` package and a HYDAT database. Leave blank if using `data` argument.
percentiles	Numeric vector of percentiles to calculate. Set to `NA` if none required. Default `c(10,90)`.
roll_days	Numeric value of the number of days to apply a rolling mean. Default `1`.
roll_align	Character string identifying the direction of the rolling mean from the specified date, either by the first (`'left'`), last (`'right'`), or middle (`'center'`) day of the rolling n-day group of observations. Default `'right'`.
water_year_start	Numeric value indicating the month (`1` through `12`) of the start of water year for analysis. Default `1`.
start_year	Numeric value of the first year to consider for analysis. Leave blank to use the first year of the source data.
end_year	Numeric value of the last year to consider for analysis. Leave blank to use the last year of the source data.
exclude_years	Numeric vector of years to exclude from analysis. Leave blank to include all years.
months	Numeric vector of months to include in analysis (e.g. `6:8` for Jun-Aug). Leave blank to summarize all months (default `1:12`).
transpose	Logical value indicating if each month statistic should be individual rows. Default `FALSE`.
spread	Logical value indicating if each month statistic should be the column name. Default `FALSE`.
ignore_missing	Logical value indicating whether dates with missing values should be included in the calculation. If `TRUE` then a statistic will be calculated regardless of missing dates. If `FALSE` then only those statistics from time periods with no missing dates will be returned. Default `FALSE`.

Value

A tibble data frame with the following columns:

Year

calendar or water year selected

Month

month of the year

Mean

mean of all daily flows for a given month and year

Median

median of all daily flows for a given month and year

Maximum

maximum of all daily flows for a given month and year

Minimum

minimum of all daily flows for a given month and year

P'n'

each n-th percentile selected for a given month and year

Default percentile columns:

P10

10th percentile of all daily flows for a given month and year

P90

90th percentile of all daily flows for a given month and year

Transposing data creates a column of 'Statistics' for each month, labeled as 'Month-Statistic' (ex "Jan-Mean"), and subsequent columns for each year selected. Spreading data creates columns of Year and subsequent columns of Month-Statistics (ex 'Jan-Mean').

Examples

# Run if HYDAT database has been downloaded (using tidyhydat::download_hydat())
if (file.exists(tidyhydat::hy_downloaded_db())) {

# Calculate statistics using a data frame and data argument with defaults
flow_data <- tidyhydat::hy_daily_flows(station_number = "08NM116")
calc_monthly_stats(data = flow_data,
                   start_year = 1980)

# Calculate statistics using station_number argument with defaults
calc_monthly_stats(station_number = "08NM116",
                   start_year = 1980)

# Calculate statistics regardless if there is missing data for a given year
calc_monthly_stats(station_number = "08NM116",
                   ignore_missing = TRUE)
                  
# Calculate statistics for water years starting in October
calc_monthly_stats(station_number = "08NM116",
                   start_year = 1980,
                   water_year_start = 10)
                  
# Calculate statistics with custom years
calc_monthly_stats(station_number = "08NM116",
                   start_year = 1981,
                   end_year = 2010,
                   exclude_years = c(1991,1993:1995))
                  
# Calculate statistics for 7-day flows, with 25 and 75th percentiles
calc_monthly_stats(station_number = "08NM116",
                   roll_days = 7,
                   percentiles = c(25,75),
                   ignore_missing = TRUE)
                   
}
#> Warning: One or more calculations included missing values and NA's were produced. Some months in some years have no data to summarize.
#> Warning: One or more calculations included missing values and NA's were produced. Filter data for complete years or months, or use to ignore_missing = TRUE to ignore missing values.
#> Warning: One or more calculations included missing values and NA's were produced. Some months in some years have no data to summarize.
#> # A tibble: 828 x 9
#>    STATION_NUMBER  Year Month  Mean Median Maximum Minimum   P25   P75
#>    <chr>          <dbl> <fct> <dbl>  <dbl>   <dbl>   <dbl> <dbl> <dbl>
#>  1 08NM116         1949 Jan   NA     NA      NA     NA     NA    NA   
#>  2 08NM116         1949 Feb   NA     NA      NA     NA     NA    NA   
#>  3 08NM116         1949 Mar   NA     NA      NA     NA     NA    NA   
#>  4 08NM116         1949 Apr    7.27   6.64   13.6    1.93   3.51 11.2 
#>  5 08NM116         1949 May   26.2   27.8    41.1   13.1   15.1  34.2 
#>  6 08NM116         1949 Jun    9.63   7.45   20.8    3.59   4.08 14.9 
#>  7 08NM116         1949 Jul    1.93   1.56    4.29   0.950  1.24  2.00
#>  8 08NM116         1949 Aug    1.25   1.23    1.68   0.882  1.09  1.35
#>  9 08NM116         1949 Sep    1.37   1.39    1.97   0.838  1.01  1.64
#> 10 08NM116         1949 Oct   NA     NA      NA     NA     NA    NA   
#> # ... with 818 more rows