# R Online Test

## For Jobseekers

Practice your skills and earn a certificate of achievement when you score in the top 25%.

Take a Practice Test## For Companies

Test candidates with real-world problems and interview the best ones.

Sign Up to Offer this Test## About the test

The R online test assesses knowledge of programming in the R language through a series of live coding tasks that focus on data analysis.

The assessment includes work-sample tasks such as:

- Generating statistical reports.
- Working with Vectors and DataFrames.
- Cleaning data to avoid incorrect records.

A good R developer needs a solid understanding of the R programming language and the ability to take advantage of its rich set of built-in functions to support statistical and data analysis.

## Sample public questions

A company stores login data and passwords in two different containers:

- A
*DataFrame*with the columns:*id*,*name*, and*verified*. - A matrix where each row contains, in order:
*id*and*password*.

The first column of any row in the matrix corresponds to the *id *column in the *DataFrame*. Elements on the same row/index in both the *DataFrame *and the *matrix *have the same *id*.

Implement the function *loginTable* that accepts these two containers and returns a new *DataFrame *that contains the following columns:

- The
*id*column from the*idNameVerified DataFrame*. - The
*name*column from the*idNameVerified DataFrame*. - A new column, called
*password*that contains the password from the*idPassword*matrix.

For example, the following code snippet:

```
idNameVerified = data.frame(id = c(1, 2),
name = c("JohnDoe", "AnnFranklin"),
verified = c(TRUE, FALSE))
idPassword = matrix(c(1, 2, 987340123, 187031122),
nrow=2,
ncol=2)
print(loginTable(idNameVerified,idPassword))
```

Should print:

id name password 1 1 JohnDoe 987340123 2 2 AnnFranklin 187031122

Implement the function *findRoots* to find the roots of the quadratic equation: ax^{2} + bx + c = 0. The function should return a vector containing roots in any order. If the equation has only one solution, the function should return that solution as both elements of the vector. The equation will always have at least one solution.

The roots of the quadratic equation can be found with the following formula:

For example, *findRoots(2, 10, 8)* should return a vector containing *(-1, -4)* or *(-4, -1)* as the roots of the equation 2x^{2} + 10x + 8 = 0 are -1 and -4.

## For jobseekers: get certified

Earn a free certificate by achieving top 25% on the R test with public questions.

Take a Certification Test## Sample silver certificate

Sunshine Caprio

Java and SQL TestDomeCertificate

## For companies: premium questions

Buy TestDome to access premium questions that can't be practiced.

Get money back if you find any premium question answered online.

### 5 more premium R questions

Recruitment Analytics, Median Height, Grocery Stores, Class Grades, Vectors.

### Skills and topics tested

- R
- Vector
- Data Cleaning
- DataFrame
- Linear Regression
- Grouping
- Arithmetic
- Iteration

### For job roles

- R Developer

### Sample candidate report

## What others say

Simple, straight-forward technical testing

TestDome is simple, provides a reasonable (though not extensive) battery of tests to choose from, and doesn't take the candidate an inordinate amount of time. It also simulates working pressure with the time limits.

Jan Opperman, Grindrod Bank

### Product reviews

## Used by

## Solve all your skill testing needs

### 150+ Pre-made tests

From web development and database administration to project management and customer support. See all pre-made tests.

### 90+ skills

From JavaScript and SQL to English and customer support. See all questions to filter by skill.

### Multi-skills Test

Mix questions for different skills or even custom questions in one test. See an example.

## How TestDome works

Choose a pre-made test

or create a custom test

Invite candidates via

email, URL, or your ATS

Candidates take

a test remotely

Sort candidates and

get individual reports