Calculates means, medians, maximums, minimums, and percentiles for each day of the year of flow values from a daily streamflow data set. Can determine statistics of rolling mean days (e.g. 7-day flows) using the roll_days argument. Note that statistics are based on the numeric days of year (1-365) and not the date of year (Jan 1 - Dec 31). Calculates statistics from all values, unless specified. Returns a tibble with statistics.

calc_daily_stats(
data,
dates = Date,
values = Value,
groups = STATION_NUMBER,
station_number,
percentiles = c(5, 25, 75, 95),
roll_days = 1,
roll_align = "right",
water_year_start = 1,
start_year,
end_year,
exclude_years,
complete_years = FALSE,
months = 1:12,
transpose = 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. 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. 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. 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. 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. Numeric vector of percentiles to calculate. Set to NA if none required. Default c(5,25,75,95). Numeric value of the number of days to apply a rolling mean. Default 1. 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'. Numeric value indicating the month (1 through 12) of the start of water year for analysis. Default 1. Numeric value of the first year to consider for analysis. Leave blank to use the first year of the source data. Numeric value of the last year to consider for analysis. Leave blank to use the last year of the source data. Numeric vector of years to exclude from analysis. Leave blank to include all years. Logical values indicating whether to include only years with complete data in analysis. Default FALSE. Numeric vector of months to include in analysis (e.g. 6:8 for Jun-Aug). Leave blank to summarize all months (default 1:12). Logical value indicating whether to transpose rows and columns of results. Default FALSE. 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:

Date

date (MMM-DD) of daily statistics

DayofYear

day of year of daily statistics

Mean

daily mean of all flows for a given day of the year

Median

daily mean of all flows for a given day of the year

Maximum

daily mean of all flows for a given day of the year

Minimum

daily mean of all flows for a given day of the year

P'n'

each daily n-th percentile selected of all flows for a given day of the year

Default percentile columns:
P5

daily 5th percentile of all flows for a given day of the year

P25

daily 25th percentile of all flows for a given day of the year

P75

daily 75th percentile of all flows for a given day of the year

P95

daily 95th percentile of all flows for a given day of the year

Transposing data creates a column of "Statistics" and subsequent columns for each year selected.

## Examples

# Run if HYDAT database has been downloaded (using tidyhydat::download_hydat())

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

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

# Calculate daily statistics regardless if there is missing data for a given day of year
calc_daily_stats(station_number = "08NM116",
ignore_missing = TRUE)

# Calculate daily statistics using only years with no missing data
calc_daily_stats(station_number = "08NM116",
complete_years = TRUE)

# Calculate daily statistics for water years starting in October between 1980 and 2010
calc_daily_stats(station_number = "08NM116",
start_year = 1980,
end_year = 2010,
water_year_start = 10)

# Calculate daily statistics with custom years and removing certain years
calc_daily_stats(station_number = "08NM116",
start_year = 1981,
end_year = 2010,
exclude_years = c(1991,1993:1995))

# Calculate daily statistics for 7-day flows for July-September months only,
# with 25 and 75th percentiles starting in 1980
calc_daily_stats(station_number = "08NM116",
start_year = 1980,
roll_days = 7,
months = 7:9,
percentiles = c(25,75))

}
#> # A tibble: 92 x 9
#>    STATION_NUMBER Date   DayofYear  Mean Median Minimum Maximum   P25   P75
#>    <chr>          <chr>      <dbl> <dbl>  <dbl>   <dbl>   <dbl> <dbl> <dbl>
#>  1 08NM116        Jul-01       182 14.0   11.0    0.717    39.6  6.79 18.6
#>  2 08NM116        Jul-02       183 13.3   10.3    0.730    40.1  6.29 17.2
#>  3 08NM116        Jul-03       184 12.7    9.84   0.932    39.6  6.20 15.8
#>  4 08NM116        Jul-04       185 12.2    9.15   1.35     40.4  6.34 14.7
#>  5 08NM116        Jul-05       186 11.7    8.70   1.41     41.4  6.02 13.9
#>  6 08NM116        Jul-06       187 11.2    8.13   1.31     44.5  5.73 13.2
#>  7 08NM116        Jul-07       188 10.7    7.49   1.10     44.6  5.31 11.9
#>  8 08NM116        Jul-08       189 10.2    6.62   0.914    44.8  5.26 11.1
#>  9 08NM116        Jul-09       190  9.49   6.05   0.747    42.3  4.93 10.8
#> 10 08NM116        Jul-10       191  8.96   5.83   0.628    40.1  4.53  9.96
#> # ... with 82 more rows