Category: R FAQS
R Frequently Asked Questions (FAQS)
Important Frequently Asked Questions about R
This post is about some frequently asked Questions about R Language. These questions will help you prepare for examinations and interviews.
Question: What is a Compiler in R Language?
Answer: A compiler is software that transforms computer code (source code) to another computer language (target language, i.e., object code).
Question: What is a package in R Language?
Answer: The R package is a collection of R functions, compiled code, sample data, and help documentation. The R packages are stored in a directory called “library” in the R environment. The R language also installed a set of packages during installation.
Question: What is JIT?
Answer: JIT standards for “Just in Time” compiler. It is a method to improve the run-time performance of a computer program.
Question: What is procedural Programming in R Language?
Answer: Procedural programming is derived from structured programming and it is based on the concept of procedure call. Procedures are also known as routines, subroutines, or functions. It contains a series of computational steps to be carried out. Any procedure may be called (at any point) during a program’s execution.
Question: What is the recycling of elements in a vector?
Answer: When a mathematical operation (such as addition, subtraction, multiplication, division, etc) is performed on two vectors of different lengths (the number of elements in both vectors is different), the element having a shorter length is reused to complete the mathematical operations.
vect1 <- c(4, 1, 4, 5, 6, 9) vect2 <- c(2, 5) vect1 * vect2 ### 8, 5, 8, 25, 12, 45
The elements of vect2 are recycled to complete the operation of all elements of vect1.
Question: What is the difference between a data frame and a matrix in R Language?
Answer: In R, the data frame contains heterogeneous data (different columns of the data frame may have different types of variable) while a matrix contains homogenous data (all the columns of the matrix have the same type of variable). In a matrix, similar data types can be stored while in a data frame, different types of data can be stored.
See Questions about R language Missing Values
R Language: A Quick Reference – IV
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 – IV.
This R Language: A Quick Reference contains R commands about performing different descriptive statistics on vectors, matrices, lists, data frames, arrays, and factors.
Basic Descriptive Statistics in R Language
| 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
| 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
| 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
| 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
| 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 |
R Language: A Quick Reference – III
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: A Quick Reference contains R commands about subsetting of vectors, matrices, lists, data frames, arrays, and factors. It also discusses about setting the different properties related to R language data types.
Subsetting Vectors in R Language
| 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
| 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
| 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
| 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] = dfv | 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 |
R Language: A Quick Reference – II
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 about setting the different properties related to R language data types.
Creating Vectors in R Language
| 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
| 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
| 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
| 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
| R Command | Short Description |
|---|---|
| data.frame(n1=x1, n2=x2, ….) | Creates a data frame |
R Language Data Type Properties
| 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 |
