### R Quick Reference Guide

R language: A Quick Reference Guide about learning R Programming with a short description of the widely used commands. It will help the learner and intermediate user of the R Programming Language to get help with different functions quickly. This Quick Reference is classified into different groups. Let us start with R Language: A Quick Reference – IV.

This Quick Reference will help in performing different descriptive statistics on vectors, matrices, lists, data frames, arrays, and factors.

## Table of Contents

### Basic Descriptive Statistics in R Language

The following is the list of widely used functions that are further helpful in computing descriptive statistics. The functions below are not direct descriptive statistics functions, however, these functions are helpful to compute other descriptive statistics.

R Command | Short Description |
---|---|

sum(x1, x2, … , xn) | Computes the sum/total of $n$ numeric values given as argument |

prod(x1, x2, … , xn) | Computes the product of all $n$ numeric values given as argument |

min(x1, x2, … , xn) | Gives smallest of all $n$ values given as argument |

max(x1, x2, …, xn) | Gives largest of all $n$ values given as argument |

range(x1, x2, … , xn) | Gives both the smallest and largest of all $n$ values given as argument |

pmin(x1, x2, …) | Returns minima of the input values |

pmax(x1, x2, …) | Returns maxima of the input values |

### Statistical Descriptive Statistics in R Language

The following functions are used to compute measures of central tendency, measures of dispersion, and measures of positions.

R Command | Short Description |
---|---|

mean(x) | Computes the arithmetic mean of all elements in $x$ |

sd(x) | Computes the standard deviation of all elements in $x$ |

var(x) | Computes the variance of all elements in $x$ |

median(x) | Computes the median of all elements in $x$ |

quantile(x) | Computes the median, quartiles, and extremes in $x$ |

quantile(x, p) | Computes the quantiles specified by $p$ |

### Cumulative Summaries in R Language

The following functions are also helpful in computing the other descriptive calculations.

R Command | Short Description |
---|---|

cumsum(x) | Computes the cumulative sum of $x$ |

cumprod(x) | Computes the cumulative product of $x$ |

cummin(x) | Computes the cumulative minimum of $x$ |

cummax(x) | Computes the cumulative maximum of $x$ |

### Sorting and Ordering Elements in R Language

The sorting and ordering functions are useful in especially non-parametric methods.

R Command | Short Description |
---|---|

sort(x) | Sort the all elements of $x$ in ascending order |

sort(x, decreasing = TRUE) | Sor the all elements of $x$ in descending order |

rev(x) | Reverse the elements in $x$ |

order(x) | Get the ordering permutation of $x$ |

### Sequence and Repetition of Elements in R Language

These functions are used to generate a sequence of numbers or repeat the set of numbers $n$ times.

R Command | Short Description |
---|---|

a:b | Generates a sequence of numbers from $a$ to $b$ in steps of size 1 |

seq(n) | Generates a sequence of numbers from 1 to $n$ |

seq(a, b) | Generates a sequence of numbers from $a$ to $b$ in steps of size 1, it is the same as a:b |

seq(a, b, by=s) | Generates a sequence of numbers from $a$ to $b$ in steps of size $s$. |

seq(a, b, length=n) | Generates a sequence of numbers having length $n$ from $a$ to $b$ |

rep(x, n) | Repeats the elements $n$ times |

rep(x, each=n) | Repeats the elements of $x$, each element is repeated $n$ times |