lambda.tools (version 1.0.7)

item: Safely get an element from a vector

Description

This function guarantees a vector of length > 1 as the return value of an indexing operation.

Arguments

v

A sequence

idx

The index of the element to extract

Value

• Either the value of x[idx] or NA for invalid index values

Usage

item(v, idx)

Details

Standard R indexing yields different results depending on the input. When either an empty vector or a NULL is passed to the indexing operator, an empty vector is returned. However, if the index is NA, the return value will be a vector of NAs having the same length as the original vector. This inconsistent behavior requires special handling whenever the index value is computed dynamically.

This function is designed to create a consistent return value for a bad index value, which is defined as {NULL, NA, vector of length 0}. If any of these values are used as the index, then NA is returned instead of an empty vector.

Examples

# Compare default behavior with item
(1:10)[NA]
item(1:10, NA)

# Negative indices are still allowed
item(1:10, -2)