179 lines
3.1 KiB
Plaintext
179 lines
3.1 KiB
Plaintext
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---
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description: k files
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globs: *.k
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---
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Use ngn/k for k files.
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ngn/k Cheatsheet
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Basics
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Running k Code
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1+2 / Addition
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3-1 / Subtraction
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2*3 / Multiplication
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10%3 / Division (floating point if needed)
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Right-to-Left Evaluation
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1+5*2-2 / Evaluates as: 1 + (5 * (2 - 2)) = 1
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1+(5*2)-2 / Parentheses force standard order
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Assignments
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a: 10 / Assign 10 to a
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b: a+5 / Assign 15 to b
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Comments
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/ This is a comment
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Data Types
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Atoms (Scalars)
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42 / Integer
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3.14 / Float
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"c" / Character
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`symbol / Symbol
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Vectors (1D Arrays)
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1 2 3 4 / Integer vector
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1.2 3.4 5.6 / Float vector
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"abcd" / Character vector
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`foo`bar`baz / Symbol vector
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Lists (Nested Arrays)
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(1 2 3; 4 5) / List of vectors
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("abc"; 1 2 3) / Mixed-type list
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Vectorized Operations
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Unlike traditional languages, operations apply element-wise:
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1 2 3 + 4 / 5 6 7
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2 * 1 2 3 / 2 4 6
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Operations also work on nested lists:
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(1 2; 3 4) + 10 / (11 12; 13 14)
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Indexing
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x: 10 20 30 40
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x[2] / Returns 30
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x[1 3] / Returns 20 40
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For lists:
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l: (10 20 30; "abc"; `sym)
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l[1] / Returns "abc"
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l[0][2] / Returns 30
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Built-in Verbs
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Arithmetic
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+ Flip (transpose matrix), Add
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- Negate (monadic), Subtract (dyadic)
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* First (monadic), Multiply (dyadic)
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% Square root (monadic), Divide (dyadic)
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! Factorial (monadic), Modulo (dyadic)
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Comparisons
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< Less than, Ascend (monadic)
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> Greater than, Descend (monadic)
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= Equal, Group (monadic)
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~ Match (deep equality), Not (monadic)
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Logical Operations
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& Min (dyadic), Where (monadic)
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| Max (dyadic), Reverse (monadic)
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Data Manipulation
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, Concat, Enlist (monadic)
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^ Without (dyadic), Null (monadic)
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# Reshape (dyadic), Length (monadic)
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_ Drop (dyadic), Floor (monadic)
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$ Cast (dyadic), String (monadic)
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? Find (dyadic), Unique (monadic), Random selection
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@ Apply (indexing and function calls)
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. Drill (deep indexing)
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Adverbs (Higher-order Operations)
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Each (')
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2*'1 2 3 / Returns 2 4 6
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Reduce (/)
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+/1 2 3 / Returns sum: 6
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Scan (\)
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+\1 2 3 / Returns running sum: 1 3 6
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Each-Prior (':)
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+': 1 2 3 4 / Returns 1 3 5 7 (pairwise sum)
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Each-Right (/:)
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1 2*/:3 4 / Returns (3 6; 4 8)
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Each-Left (\:)
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1 2*\:3 4 / Returns (3 4; 6 8)
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Window (i':)
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3':!10 / Sliding window
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Stencil (i f':)
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3+/':!10 / Stencil sum
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Bin Search (X')
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1 3 5 7 9'8 9 0 / Bin classification
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Array-Oriented Typing vs Traditional Languages
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Key Differences
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Operations are implicitly vectorized
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No need for loops to apply operations to arrays
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Example: 2 * 1 2 3 produces 2 4 6 directly
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Data is homogeneously typed
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Unlike Python lists, k enforces consistent typing in arrays
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Example: 1 2 "a" would cause an error
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Functions behave like array transformations
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Monadic (single argument) and dyadic (two arguments) versions exist
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Example: * 1 2 3 returns 1 (first element), 1*2 3 returns 2 3
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Indexing and function application use the same syntax
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f[2] calls f with argument 2
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arr[2] retrieves index 2 from arr
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Example: Simple Statistics
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x: 1 2 3 4 5
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mean: (+/x) % #x / Sum divided by count
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mean / this will print to screen aka return from main
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