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The practice workbook

R sticks when you write it, not when you read about it. Each problem here checks your answer the moment you run it, so you always know which skills you own and which need another rep.

New to R Interview prep Everyday fluency Statistics depth

7 minutes, between lectures

Predict the outputHard

x <- c("10", "5", "20")
as.numeric(factor(x))

[1] 1 3 2Correct · +50 XP

Featured problem sets

17 hand-picked sets, grouped by what you're practicing for.

Interview prep6 sets · 165 problems

R Interview Questions (Top 50)50 Statistics Interview Questions25 ML Interview Questions25 A/B Testing Interview Cases20 SQL to dplyr Translations30 Take-Home Simulator15

Open Interview prep →

Everyday fluency5 sets · 130 problems

Base R Speed Round50 The Regex 2020 Dates and Times Drills15 Error Triage Drills20 Data Cleaning Gauntlet25

Open Everyday fluency →

Statistics depth6 sets · 112 problems

Top 20 Bayesian Problems20 Probability Puzzles (Top 20)20 Top 25 Regression Problems25 Top 20 Time Series Problems20 The Resampling 1515 ggplot2 Recreation Challenge12

Open Statistics depth →

The Exercises Wall

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By topic

R Fundamentals0 / 397 Data Wrangling0 / 738 Visualization0 / 395 Statistics0 / 743 Time Series0 / 255 Machine Learning0 / 194 Advanced R0 / 105 Reporting0 / 48 Specializations0 / 179

Browse by topic

130 hubs in 9 topics. 7 of them end with a timed mastery quiz.

R Fundamentals 18 Data Wrangling 29 Visualization 16 Statistics 37 Time Series 6 Machine Learning 8 Advanced R 5 Reporting 2 Specializations 9

1R Fundamentals18 hubs · 397 problems · 10,855 XPVectors, data frames, functions, and the base R muscle memory everything else builds on.0 / 397 solved

1.1R Beginner Exercises0/30605 XP 1.2R apply Family0/20510 XP 1.3R Lists0/24595 XP 1.4R for Data Science Exercises0/501,245 XP 1.5R Data Frames0/17465 XP 1.6Functional Programming0/18490 XP 1.7R Vectors0/18490 XP 1.8R Control Flow0/18515 XP 1.9R Date & Time0/20540 XP 1.10OOP in R0/20590 XP 1.11R Subsetting0/20590 XP 1.12purrr Exercises0/30875 XP 1.13R Basics0/18530 XP 1.14R Functions0/18530 XP 1.15R Debugging Exercises0/18580 XP 1.16Apply Family Exercises0/20580 XP 1.17Loops vs Vectorization Exercises0/20580 XP 1.18R Strings0/18545 XP

Finished here? Take the R Fundamentals Quiz (12 min) to check what stuck.Start quiz →

Finished here? Take the R Interview Readiness Quiz (12 min) to check what stuck.Start quiz →

Finished here? Take the Functional Programming Quiz (12 min) to check what stuck.Start quiz →

2Data Wrangling29 hubs · 738 problems · 21,485 XPImport, clean, reshape, and join real datasets with dplyr, tidyr, and friends.0 / 738 solved

2.1dplyr0/15425 XP 2.2Tidyverse Exercises0/501,390 XP 2.3Data Import0/17465 XP 2.4API Calls Exercises0/17515 XP 2.5purrr0/13430 XP 2.6Missing Data in R0/19565 XP 2.7dplyr filter() & select()0/20515 XP 2.8data.table0/20540 XP 2.9dbplyr / SQL Exercises0/20565 XP 2.10Regex Exercises0/25725 XP 2.11data.table Exercises0/501,450 XP 2.12dplyr Window Functions Exercises0/25725 XP 2.13lubridate Exercises0/28775 XP 2.14stringr Exercises0/28775 XP 2.15readr Exercises0/28800 XP 2.16Data Cleaning Exercises0/28825 XP 2.17Web Scraping Exercises0/17505 XP 2.18tidyr Reshaping0/18480 XP 2.19tidyr Pivot Exercises0/18505 XP 2.20Date-Time Manipulation Exercises0/18530 XP 2.21tidyr Exercises0/30900 XP 2.22Data Wrangling Exercises0/501,430 XP 2.23dplyr Exercises0/501,430 XP 2.24dplyr Joins0/20605 XP 2.25forcats Exercises0/28890 XP 2.26dplyr group_by Exercises0/25755 XP 2.27dplyr Joins Exercises0/25805 XP 2.28dplyr group_by() & summarise()0/18570 XP 2.29tidyr Nest/Unnest Exercises0/18595 XP

Finished here? Take the dplyr Quiz (12 min) to check what stuck.Start quiz →

Finished here? Take the tidyr Quiz (12 min) to check what stuck.Start quiz →

3Visualization16 hubs · 395 problems · 11,800 XPCharts that read clearly, from a first ggplot2 bar chart to themed, faceted figures.0 / 395 solved

3.1ggplot20/15425 XP 3.2ggplot2 Themes Exercises0/20525 XP 3.3EDA Exercises0/501,335 XP 3.4ggplot2 Heatmap Exercises0/20565 XP 3.5ggplot2 Facets0/15455 XP 3.6ggplot2 Color Scales Exercises0/20615 XP 3.7leaflet Exercises0/20615 XP 3.8ggplot2 Geoms0/16455 XP 3.9ggplot2 Exercises0/501,465 XP 3.10ggplot2 Aesthetics0/18530 XP 3.11Data Viz Exercises0/25740 XP 3.12ggplot2 Facets Exercises0/20580 XP 3.13plotly Exercises0/20630 XP 3.14ggplot2 Bar Chart Exercises0/18570 XP 3.15ggplot2 Customization0/18570 XP 3.16R Visualization Project (5 charts)0/501,725 XP

Finished here? Take the ggplot2 Quiz (12 min) to check what stuck.Start quiz →

4Statistics37 hubs · 743 problems · 22,375 XPProbability, tests, confidence intervals, and regression, practiced until the output makes sense.0 / 743 solved

4.1Probability in R Exercises0/15440 XP 4.2Probability Distributions0/25685 XP 4.3Mixed Effects Exercises0/18615 XP 4.4A/B Testing Exercises0/20540 XP 4.5ANOVA Exercises0/15405 XP 4.6Linear Regression0/501,350 XP 4.7Chi-Square Exercises0/20565 XP 4.8t-Test Exercises0/20565 XP 4.9R Probability Distributions0/20590 XP 4.10Experimental Design Exercises0/20615 XP 4.11Binomial Distribution Exercises0/17480 XP 4.12Confidence Interval0/18480 XP 4.13Nonparametric Exercises0/18505 XP 4.14Multiple Testing0/18530 XP 4.15A/B Testing Exercises0/18555 XP 4.16Power Analysis Exercises0/18580 XP 4.17Correlation Exercises0/20580 XP 4.18Poisson Regression0/20580 XP 4.19Sampling Methods Exercises0/20580 XP 4.20Survey Analysis Exercises0/20605 XP 4.21broom Exercises0/20605 XP 4.22PCA Exercises0/20630 XP 4.23GLM Exercises0/22705 XP 4.24Central Limit Theorem Exercises0/16470 XP 4.25SEM Exercises0/16570 XP 4.26Logistic Regression Exercises0/25755 XP 4.27Regression Diagnostics Exercises0/25755 XP 4.28Hypothesis Testing Exercises0/25780 XP 4.29Clustering Exercises0/17495 XP 4.30Poisson Distribution Exercises0/17520 XP 4.31Ridge & Lasso Exercises0/18545 XP 4.32Post-Hoc Tests Exercises0/18570 XP 4.33Survival Analysis Exercises0/18570 XP 4.34Bayesian Statistics Exercises0/20670 XP 4.35Multiple Regression Exercises0/21695 XP 4.36Repeated Measures0/17560 XP 4.37GAM Exercises0/18635 XP

Finished here? Take the Hypothesis Testing Quiz (12 min) to check what stuck.Start quiz →

Finished here? Take the Linear Regression Quiz (12 min) to check what stuck.Start quiz →

5Time Series6 hubs · 255 problems · 7,550 XPDates, decomposition, and ARIMA forecasting drills.0 / 255 solved

5.1Exponential Smoothing Exercises0/501,385 XP 5.2Time Series Exercises0/30835 XP 5.3Forecast Evaluation Exercises0/501,525 XP 5.4Decomposition Exercises0/501,505 XP 5.5Time Series in R Exercises0/501,530 XP 5.6ARIMA Exercises0/25770 XP

Finished here? Take the Time Series Quiz (12 min) to check what stuck.Start quiz →

6Machine Learning8 hubs · 194 problems · 5,850 XPTrain, validate, and tune models: trees, forests, boosting, clustering.0 / 194 solved

6.1Machine Learning Exercises0/501,405 XP 6.2Decision Tree Exercises0/18490 XP 6.3XGBoost Exercises0/20590 XP 6.4tidymodels Exercises0/25790 XP 6.5Random Forest Exercises0/20580 XP 6.6caret Exercises0/21630 XP 6.7Clustering Exercises0/20670 XP 6.8Cross Validation Exercises0/20695 XP

Finished here? Take the Machine Learning Quiz (12 min) to check what stuck.Start quiz →

7Advanced R5 hubs · 105 problems · 3,190 XPPerformance, packages, testing, and Shiny apps.0 / 105 solved

7.1Parallel Computing Exercises0/23660 XP 7.2R Performance Exercises0/20565 XP 7.3testthat Exercises0/17480 XP 7.4R Package Development0/20630 XP 7.5Shiny Exercises0/25855 XP

Finished here? Take the Shiny Quiz (12 min) to check what stuck.Start quiz →

8Reporting2 hubs · 48 problems · 1,350 XPR Markdown documents and publication tables.0 / 48 solved

8.1gt Tables Exercises0/23650 XP 8.2R Markdown Exercises0/25700 XP

9Specializations9 hubs · 179 problems · 5,925 XPDomain practice: finance, genomics, healthcare, marketing, spatial, text.0 / 179 solved

9.1Network Analysis Exercises0/20565 XP 9.2R for Biostatistics0/20615 XP 9.3R for Healthcare Exercises0/20665 XP 9.4R for Finance Exercises0/25875 XP 9.5Text Mining Exercises0/20630 XP 9.6R for Sports Analytics0/20680 XP 9.7R for Marketing Analytics0/20730 XP 9.8Spatial Analysis Exercises0/15470 XP 9.9R for Genomics0/19695 XP

Mastery quizzes

11 timed quizzes, 12 minutes each. Each one also appears at the end of its topic above.

R Fundamentals QuizR Fundamentals · 12 min R Interview Readiness QuizR Fundamentals · 12 min Functional Programming QuizR Fundamentals · 12 min dplyr QuizData Wrangling · 12 min tidyr QuizData Wrangling · 12 min ggplot2 QuizVisualization · 12 min Hypothesis Testing QuizStatistics · 12 min Linear Regression QuizStatistics · 12 min Time Series QuizTime Series · 12 min Machine Learning QuizMachine Learning · 12 min Shiny QuizAdvanced R · 12 min