within_km: Identify rows of dataframe with observations in certain...
In LukasWallrich/rNuggets: Useful Helper Functions for (Academic) Data Analysis

within_km

R Documentation

Identify rows of dataframe with observations in certain distance from point

Description

within_km tests for each line of a dataframe with longitude and latitude variables whether the location so described is within a certain radius from a given starting point.

Usage

within_km(df, start_longitude, start_latitude, km)

Arguments

`df`	Dataframe with observations, must include latitude and longitude variables in degrees
`start_longitude`	Longitude of starting point in degrees.
`start_latitude`	Latitude of starting point in degrees.
`km`	Distance from starting point to filter line by

Details

Note that this function is very inefficient. It calculates the distance of each line to the starting point using the Haversine formula. If you need to use this regularly or on large datasets, a previous step to throw out lines that are clearly too far away based on either latitude or longitude would greatly increase efficiency.