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 – III.
This R Language Quick Reference contains R commands about subsetting of vectors, matrices, lists, data frames, arrays, and factors. It also discusses setting the different properties related to R language data types.
Subsetting Vectors in R Language
The following are ways to subset or slice the values from a vector.
| R Command | Short Description |
|---|---|
| x[1:5] | Select elements of $x$ by index |
| x[-(1:5)] | Exclude elements of $x$ by index |
| x[c(TRUE, FALSE)] | Select elements of $x$ corresponding to the True value |
| x[c(“a”, “b”)] | Select elements of $x$ by name |
Subsetting Lists in R Language
The following methods are used to subset or slice a list in R Language.
| R Command | Short Description |
|---|---|
| x[1:5] | Extracts a sublist of the list $x$ |
| x[-(1:5)] | Extract a sublist by excluding elements of list $x$ |
| x[c(TRUE, FALSE)] | Extract a sublist with logical subscripts |
| x[c(“a”, “b”)] | Extract a sublist by name |
| x[[2]] | Extract an element of the list $x$ |
| x[[“a”]] | Extract the element with the name “a” from list $x$ |
| x$a | Extract the element with the name “a” from list $x$ |
Subsetting Matrices in R Language
To subset or extract certain elements from a matrix follow the ways described below.
| R Command | Short Description |
|---|---|
| x[i, j] | Extracts elements of matrix $x$, specified by row $i$ and column $j$ |
| x[i, j] = v | Set or rest the elements of matrix $x$, specified by row $i$ and column $j$ |
| x[i, ] | Extracts $i$th row of a matrix $x$ |
| x[i, ] = v | Set or resets the $i$th row of a matrix $x$ specified by $i$th row |
| x[ , j] | Extracts the $j$ column of a matrix $x$ |
| x[ , j] = v | Sets or resets the $j$ column of matrix $x$ |
| x[i] | Subets a matrix $x$ as a vector |
| x[i] = v | Sets or resets the $i$th elements (treated as a vector operation) |
Subsetting a Data Frame in R Language
One can easily subset or slice a Data Frame in R.
| R Command | Short Description |
|---|---|
| df[i, j] | Matrix subsetting of a data frame, specified by $i$th row and $j$th column |
| df[i, j] = df | Sets or resets a subset of a data frame |
| subset(df, subset = i) | Subset of the $i$ cases/ observations of a data frame |
| subset(df, select = i) | Subset of the $i$ variables/ columns of a data frame |
| subset(df, subset=i, select=j) | Subset of the $i$ cases and $j$ variables of a data frame |
