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#' Filter the eBird data by state
#'
#' Define a filter for the eBird Basic Dataset (EBD) based on a set of
#' states. This function only defines the filter and, once all filters have
#' been defined, [auk_filter()] should be used to call AWK and perform the
#' filtering.
#'
#' @param x `auk_ebd` or `auk_sampling` object; reference to file created by
#' [auk_ebd()] or [auk_sampling()].
#' @param state character; states to filter by. eBird uses 4 to 6 character
#' state codes consisting of two parts, the 2-letter ISO country code and a
#' 1-3 character state code, separated by a dash. For example, `"US-NY"`
#' corresponds to New York State in the United States. Refer to the data frame
#' [ebird_states] for look up state codes.
#' @param replace logical; multiple calls to `auk_state()` are additive,
#' unless `replace = FALSE`, in which case the previous list of states to
#' filter by will be removed and replaced by that in the current call.
#'
#' @details It is not possible to filter by both country and state, so calling
#' `auk_state()` will reset the country filter to all countries, and vice versa.
#'
#' This function can also work with on an `auk_sampling` object if the user only
#' wishes to filter the sampling event data.
#'
#' @return An `auk_ebd` object.
#' @export
#' @family filter
#' @examples
#' # state codes for a given country can be looked up in ebird_states
#' dplyr::filter(ebird_states, country == "Costa Rica")
#' # choose texas, united states and puntarenas, cost rica
#' states <- c("US-TX", "CR-P")
#' system.file("extdata/ebd-sample.txt", package = "auk") %>%
#' auk_ebd() %>%
#' auk_state(states)
#'
#' # alternatively, without pipes
#' ebd <- auk_ebd(system.file("extdata/ebd-sample.txt", package = "auk"))
#' auk_state(ebd, states)
auk_state <- function(x, state, replace = FALSE) {
UseMethod("auk_state")
}
#' @export
auk_state.auk_ebd <- function(x, state, replace = FALSE) {
# checks
assertthat::assert_that(
is.character(state),
assertthat::is.flag(replace)
)
state <- toupper(state)
# check codes are valid
valid_codes <- state %in% auk::ebird_states$state_code
if (!all(valid_codes)) {
m <- paste0("The following state codes are not valid: \n\t",
paste(state[!valid_codes], collapse =", "))
stop(m)
}
# add states to filter list
if (replace) {
x$filters$state <- state
} else {
x$filters$state <- c(x$filters$state, state)
}
x$filters$state <- sort(unique(x$filters$state))
x$filters$country <- character()
x$filters$county <- character()
return(x)
}
#' @export
auk_state.auk_sampling <- function(x, state, replace = FALSE) {
auk_state.auk_ebd(x, state, replace)
}
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