Extract parts of an object

A wrapper for [ that handles NA indices better when using inside summarize

Usage

extr_val(x, i, allNA_NA = TRUE, na.rm = FALSE)

Arguments

x

object from which to extract element(s)

i

index specifying element to extract.

allNA_NA

logical indicating whether NA should be returned when all(is.na(i)) == TRUE.

na.rm

a logical indicating whether missing values should be removed.

Value

If allNA_NA = FALSE and na.rm = FALSE, identical to x[i].

If allNA_NA = FALSE and na.rm = TRUE, identical to x[i[!is.na(i)]].

If allNA_NA = TRUE, identical to x[i] unless all(is.na(i)) == TRUE, in which case returns NA

Details

This function was created to better handle the common situation of extracting values by index inside summarize when some indices may be NA. Often this arises when using a function to find indices of interest might fail to find any, as can sometimes happen when using which_max_gc or which_min_gc (wrappers for which.max and which.min, respectively), find_local_extrema and its wrappers first_maxima and first_minima, or find_threshold_crosses and its wrappers first_below and first_above. When all indices are NA, [ returns a vector of all NA of length length(x). Since this typically raises an undesirable warning or error from summarize, extr_val instead returns a single NA value.

An alternative (but largely superseded) use of this function is to extract a value by index after NA values have been removed. This is not applicable for any common functions with gcplyr, which all return index values for the original vector.