Returns hydrochemical data from the Watina database, either as a lazy object or as a local tibble. The values must belong to selected locations and to a specified timeframe.
get_chem( locs, con, startdate, enddate = paste(day(today()), month(today()), year(today())), conc_type = c("mass", "eq"), en_range = c(-0.1, 0.1), en_exclude_na = FALSE, en_fecond_threshold = 0.0023, collect = FALSE )
| locs | A |
|---|---|
| con | A |
| startdate | First date of the timeframe, as a string.
The string must use a formatting of the order 'day month year',
i.e. a format which can be interpreted by Examples:
|
| enddate | Last date of the timeframe, as a string.
The same formatting rule must be applied as in |
| conc_type | A string defining the type of concentration in ionic concentration variables. Either:
Note that the argument has no effect on the value of non-ion-variables. |
| en_range | Numeric vector of length 2.
Specifies the allowed range of
water sample electroneutrality for ion-variable measurements (see Details).
Both vector elements must be within the range |
| en_exclude_na | Logical. Should ion-variable measurements of water samples with missing electroneutrality value be omitted? Defaults to FALSE. A missing electroneutrality value is the consequence of one or more missing values of ionic concentration variables that are needed for electroneutrality calculation of the water sample. Note that this argument has no effect on the selection of non-ion variable measurements, which are always returned. |
| en_fecond_threshold | A number (with a sensible default).
May be set to
|
| collect | Should the data be retrieved as a local tibble?
If |
By default, a tbl_lazy object.
With collect = TRUE,
a local tibble is returned.
(TO BE ADDED: Explanation on the variable names of the returned object)
(TO BE ADDED: Explanation on the different abbreviations in the column 'chem_variable')
The timeframe is a selection interval between
a given startdate and enddate.
The water samples must meet a specified electroneutrality
condition, set by en_range.
This condition is however ignored when the sample's iron (meq/l) /
conductivity (µS/cm) ratio exceeds en_fecond_threshold (use
en_fecond_threshold = NA if you don't want this to happen).
Further, water samples are included by default if their
electroneutrality is NA (this is controlled by the
en_exclude_na argument).
Finally, please note that measurements of non-ion variables are always returned!
To retrieve all data from all water samples, use en_range = c(-1, 1).
TO BE ADDED: What is electroneutrality and why is it used as a criterion?
Up to and including watina 0.3.0, the result was sorted according to
loc_code, date and chem_variable, both for the lazy query and the
collected result.
Later versions avoid sorting in case of a lazy result, because
otherwise, when using the result inside another lazy query, this led to
'ORDER BY' constructs in SQL subqueries, which must be avoided.
If you like to print the lazy object in a sorted manner, you must add
%>% arrange(...) yourself.
if (FALSE) { watina <- connect_watina() library(dplyr) mylocs <- get_locs(watina, area_codes = "ZWA") mylocs %>% get_chem(watina, "1/1/2017") %>% arrange(loc_code, date, chem_variable) mylocs %>% get_chem(watina, "1/1/2017", collect = TRUE) mylocs %>% get_chem(watina, "1/1/2017", conc_type = "eq") %>% arrange(loc_code, date, chem_variable) # compare the number of returned rows: mylocs %>% get_chem(watina, "1/1/2017") %>% count mylocs %>% get_chem(watina, "1/1/2017", en_fecond_threshold = NA) %>% count mylocs %>% get_chem(watina, "1/1/2017", en_exclude_na = TRUE) %>% count mylocs %>% get_chem(watina, "1/1/2017", en_exclude_na = TRUE, en_fecond_threshold = NA) %>% count mylocs %>% get_chem(watina, "1/1/2017", en_range = c(-1, 1)) %>% count # joining results to mylocs: mylocs %>% get_chem(watina, "1/1/2017") %>% left_join(mylocs %>% select(-loc_wid), .) %>% collect %>% arrange(loc_code, date, chem_variable) # Disconnect: dbDisconnect(watina) }