Sampling a Subset of DataFrame by Group with Sample Size Equal to Another Subset of the DataFrame

Understanding the Issue with Subsetting R Data Frame Results in Mysterious NA Rows

Understanding the Issue with Subseting Data from an Excel Sheet in R

Subset Data for a Specific Column with ddply: A Deep Dive in R

How to Replace Missing Values with Means in R: A Comparative Analysis of plyr, data.table, and dplyr Approaches

Subsetting Rows for Selecting on More Than One Value Using Droplevels in R