For a dataset as returned by get_chem,
return summary statistics (data availability and/or
numeric properties) of
the specified hydrochemical variables, for each location.
eval_chem( data, chem_var = c("P-PO4", "N-NO3", "N-NO2", "N-NH4", "HCO3", "SO4", "Cl", "Na", "K", "Ca", "Mg", "Fe", "Mn", "Si", "Al", "CondF", "CondL", "pHF", "pHL"), type = c("avail", "num", "both"), uniformity_test = FALSE )
| data | An object returned by |
|---|---|
| chem_var | A character vector to select chemical variables for which
statistics will be computed.
To specify chemical variables, use the
codes from the column |
| type | A string defining the requested type of summary statistics. See section 'Value'. Either:
|
| uniformity_test | Should the availability statistic
|
A tibble with variables loc_code (see get_locs),
chem_variable (character; see Details)
and summary statistics (at the level
of loc_code x chem_variable) depending on the state of
type
(type = "both" combines both cases):
With type = "avail" (the default):
nryears: number of calendar years for which the
chemical variable is available (on one date at least)
nrdates: number of dates at which the
chemical variable is available
firstdate: earliest date at which the
chemical variable is available
lastdate: latest date at which the
chemical variable is available
timespan_years: duration as years from the first calendar year
(year of firstdate) to the last calendar year
(year of lastdate) with data available
timespan_totalspan_ratio: the ratio of timespan_years to
the 'total span', which is the duration as years from the first to the last
calendar year for the whole of data.
nryears_totalspan_ratio: the ratio of nryears to
the 'total span'
pval_uniform_totalspan: Only returned with
uniformity_test = TRUE.
p-value of an exact, one-sample two-sided
Kolmogorov-Smirnov test for the discrete uniform distribution of the calendar
years with data of the chemical variable available within the series
of consecutive calendar years defined by the 'total span' (see above).
The smaller the p-value,
the less uniform the years are spread within the total span.
A perfectly uniform spread results in a p-value of 1.
With type = "num": summary statistics based on the chemical values,
i.e. excluding the 'combined' level:
val_min: minimum value
val_pct10, val_pct25, val_pct50,
val_pct75, val_pct90: percentiles
val_max: maximum value
val_range: range
val_mean: mean
val_geometric_mean: geometric mean.
Only calculated when
all values are strictly positive.
unit
prop_below_loq: the proportion of measurements below the limit
of quantification (as derived from below_loq == TRUE),
i.e. relative to the total number of measurements
for which below_loq is not NA.
This statistic neglects measurements with value NA for
below_loq!
If all measurements have value NA for
below_loq, this statistic is set to NA.
For the availability statistics, an extra level
"combined" is added in the column chem_variable whenever the
arguments data and
chem_var imply more than one
chemical variable to be investigated.
This 'combined' level defines data availability for a water sample as the
availability of data for all corresponding chemical variables.
Other functions to evaluate locations:
eval_xg3_avail(),
eval_xg3_series()
if (FALSE) { watina <- connect_watina() library(dplyr) mylocs <- get_locs(watina, area_codes = "ZWA") mydata <- mylocs %>% get_chem(watina, "1/1/2010") mydata %>% arrange(loc_code, date, chem_variable) mydata %>% pull(date) %>% lubridate::year(.) %>% (function(x) c(firstyear = min(x), lastyear = max(x))) mydata %>% eval_chem(chem_var = c("P-PO4", "N-NO3", "N-NO2", "N-NH4")) %>% arrange(desc(loc_code)) mydata %>% eval_chem(chem_var = c("P-PO4", "N-NO3", "N-NO2", "N-NH4"), type = "both") %>% arrange(desc(loc_code)) %>% as.data.frame() %>% head(10) mydata %>% eval_chem(chem_var = c("P-PO4", "N-NO3", "N-NO2", "N-NH4"), uniformity_test = TRUE) %>% arrange(desc(loc_code)) %>% select(loc_code, chem_variable, pval_uniform_totalspan) # Disconnect: dbDisconnect(watina) }