R language: A Quick Reference is 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 – II.

This R Language: A Quick Reference contains R commands about creating vectors, matrices, lists, data frames, arrays, and factors. It also discusses setting the different properties related to R language data types.

### Creating Vectors in R Language

The creation of a row or column vector in the R Language is very important. One can easily create a vector of numbers, characters/ strings, complex numbers, and logical values, and can concatenate the elements.

R command | Short Description |
---|---|

c(a1, a2, …, an) | Concatenates all $n$ elements to a vector |

logical(n) | Creates a logical vector of length $n$ (containing false) |

numeric(n) | Creates a numeric vector of length $n$ (containing zeros) |

character(n) | Creates a character vector of length $n$ (containing an empty string) |

complex(n) | Creates a complex vector of length $n$ (containing zeros) |

### Creating Lists in R Language

Creating Lists in R is important as it can store different types of data and even lists. A vector can also be used to create a list of $k$ elements.

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

list(e1, e2, … ek) | Combines all $k$ elements as a list |

vector(k, “list”) | Creates a list of length $k$ (the elements are all NULL) |

### Creating Matrices in R Language

Two-dimensional data can be created using the matrix command in R.

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

matrix(x, nr = r, nc = c) | Creates a matrix from $x$ (column as major order) |

matrix(x, nr = r, nc = c) | Creates a matrix from $x$ (row as major order) |

### Creating Factors in R Language

To create categorical variables, R has a concept of factors as variables. All factors have levels that may have ordered factors.

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

factor(x) | Creates a factor from the values of variable $x$ |

factor(x, levels = 1) | Creates a factor with the given level set from the values of the variable $x$ |

ordered(x) | Creates an ordered factor with the given level set from the values of the variable $x$ |

levels(x) | Gives the levels of a factor or ordered factor |

levels(x) = v | Set or reset the levels of a factor or ordered factor |

### Creating a Data Frame in R Language

A data frame is a tabular data format used for statistical data analysis. The format of the data is like data entered in spreadsheets for data analysis.

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

data.frame(n1=x1, n2=x2, ….) | Creates a data frame |

### R Language Data Type Properties

Every data object has different properties. These properties can be used to find out the number of rows in a vector or matrix, the number of columns, names of rows and columns of a matrix or data frame.

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

length(x) | Gives the number of elements in a variable $x$ |

mode(x) | Tells about the data type of the variable $x$ |

nrow(x) | Displays the number of rows of a vector, array, or data frame $x$ |

ncol(x) | Displays the number of columns (variable) of a vector, array, or data frame $x$ |

dim(x) | Displays the dimension (number of rows and columns) of a matrix, data frame, array, or list $x$ |

row(x) | Matrix of row indices for matrix-like object $x$ |

col(x) | Matrix of column indices for matrix-like object $x$ |

rownames(x) | Get the row names of the matrix-like object $x$ |

rownames(x)=v | Set the row names of the matrix-like object $x$ to $v$ |

colnames(x) | Get the column names of the matrix-like object $x$ |

colnames(x)=v | Set the column names of the matrix-like object $x$ to $v$ |

dimnames(x) | Get both the row and column names (in a matrix, data frame, or list) |

dimnames(x)=list(rn, cn) | Set both the row and column names |

names(x) | Gives the names of $x$ |

namex(x)=v | Sets or resets the names of $x$ to $v$ |

names(x)=NULL | removes the names from $x$ |

row.names(df) | Gives the observation names from a data frame |

row.names(df)=v | Sets or resets the observation names of a data frame |

names(df) | Gives the variables names from a data frame |

names(df)=v | Sets or resets the variable names of a data frame |