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R

294 problems27 sections📅 2026 curriculum

Learn R by typing real data-analysis code.

Type through R for data work: vectorized operations, data frames, factors, the |> pipe, apply-family functions, and built-in statistics. Each snippet is idiomatic R, and an AI tutor explains every line — why vectorization beats a loop, how a data frame column is really a vector — so the analyst's mental model forms as you build typing speed.

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Run R on your machine

1. Install the toolchain

brew install r # or: sudo apt install r-base

2. Save your code as hello.R, then compile & run

Rscript hello.R

Official install docs ↗

progress by section

1Fundamentals0/12start →

Assignment with <-for loop Define a function if / else print and cat Basic types Vectors with c()while loop Vectorized ifelse()Membership with %in%Missing values with is.na()seq and rep

2Strings In Depth0/12start →

toupper and tolower nchar paste and paste0 trimws grepl startsWith and endsWith substr formatC sub and gsub sprintf strsplit In-place substr<-

3Values & References0/8start →

Arguments are copied Copy-on-modify Lists copy too Reassign the result Superassignment <<-Environments are references Shared environment tracemem

4Slices & Arrays0/10Unlock →

Range slice v[1:3]Slice assignment Slice by name head and tail Logical indexing Negative indices seq_along Slice via which()Strided slice subset()

5Data structures0/14Unlock →

Atomic vectors Vector indexing append()$ access Lists Matrices Named vectors which()Type coercion in c()Factors Building a list [[ ]] versus [ ]Matrix indexing Vector recycling

6Iterators0/12Unlock →

for loop Filter lapply sapply Vectorization vs loops apply Map mapply outer()Reduce with accumulate tapply vapply

7Closures0/12Unlock →

Default arguments Functions are values Anonymous functions Capturing the environment Filter do.call Function factory Map match.arg Reduce Varargs with ...Stateful closure

8Error Handling0/13Unlock →

Diagnostic message Raise an error try()Emit a warning tryCatch finally tryCatch an error tryCatch a warning simpleCondition on.exit cleanup Custom condition class signalCondition withCallingHandlers withRestarts

9Conversions0/10Unlock →

as.character as.integer as.numeric as.logical Type checks as.Date format numbers sprintf strtoi with a base Factor to number gotcha

10Math0/14Unlock →

Min, max, range Roots and powers Math constants Sums and products Exponentials and logs Modulo and integer division Rounding Factorial and choose Descriptive stats Trigonometry Vector angle Greatest common divisor Parallel min and max Primality test

11Data I/O0/12Unlock →

Split one CSV line Read and write lines CSV round trip Read a whitespace table Parse an in-memory CSV Assemble lines Aligned table Parse key=value Tolerant numeric parse Whitespace to matrix Fixed-width fields Build JSON by hand

12Linear Algebra0/14Unlock →

Build a matrix Scale a matrix Transpose Combine matrices Diagonals and identity Row and column reductions Apply over margins Determinant Matrix multiply Outer product Cross product Solve a linear system Matrix inverse Eigenvalues

13Text Processing0/10Unlock →

Count words Character frequency Find and replace Pad and format numbers Reverse word order Count vowels Count a substring Longest word Title case Edit distance

14Date & Time0/10Unlock →

Current date and time Parse a date Day of the week Difference between dates Format a date Leap year Parse a timestamp Unix epoch seconds Sequence of dates Parse a custom format

15Algorithms0/10Unlock →

Euclid's GCD Binary search Memoized Fibonacci Linear congruential generator Merge two sorted vectors Fisher-Yates shuffle Two-pointer pair sum Two-sum with a lookup Maximum subarray Recursive quicksort

16Sorting Algorithms0/10Unlock →

Built-in sort and order Check if sorted Bubble sort Sort by a custom key Insertion sort Selection sort Counting sort Sort by two keys Merge sort Quicksort

17Idioms0/10Unlock →

Vectorized ifelse %in% membership Vectorization apply family over loops invisible NA handling Native pipe do.call match.arg Reduce

18OOP & Traits0/14Unlock →

S3 class attribute Custom print method S3 default method Custom S3 generic S3 print dispatch Custom format method S4 setClass and new Reference class fields S3 inheritance and NextMethod S4 generic and method S4 inheritance with contains S4 show method S4 validity check Reference class methods

19Design Patterns0/12Unlock →

Command Factory Strategy Builder Decorator Dependency injection Singleton Lazy initialization Observer State Template method Actor

20Data Frames0/16Unlock →

Add a column Create a data frame Index rows and columns Inspect structure Filter rows Drop missing rows The subset helper Summarize a frame Apply over columns Sort rows by a column Split into groups Group with tapply Transform columns Group and summarize Join two frames Stack a list of frames

21Statistics0/14Unlock →

Central tendency Reproducible randomness Spread Random draws Quantiles and summary Random sampling Frequency tables Correlation and covariance Z-score scaling Grouped aggregation Kernel density Linear regression Prediction t-test

22Array0/10Unlock →

Contains Duplicate Two Sum Best Time to Buy and Sell Stock Maximum Subarray Container With Most Water Find Minimum in Rotated Sorted Array Product of Array Except Self Maximum Product Subarray Search in Rotated Sorted Array 3Sum

23Binary0/5Unlock →

Missing Number Number of 1 Bits Counting Bits Reverse Bits Sum of Two Integers

24String0/10Unlock →

Valid Anagram Valid Palindrome Valid Parentheses Encode and Decode Strings Group Anagrams Longest Substring Without Repeating Characters Longest Repeating Character Replacement Longest Palindromic Substring Palindromic Substrings Minimum Window Substring

25Matrix0/4Unlock →

Rotate Image Set Matrix Zeroes Spiral Matrix Word Search

26Interval0/5Unlock →

Meeting Rooms Merge Intervals Insert Interval Non-overlapping Intervals Meeting Rooms II

27Dynamic Programming0/11Unlock →

Climbing Stairs House Robber Unique Paths Coin Change House Robber II Jump Game Combination Sum IV Decode Ways Longest Common Subsequence Longest Increasing Subsequence Word Break