Basic Syntax and Data Types in KDB+ and Q

Introduction

KDB+ and its associated language, Q, offer a unique syntax and data model that is designed for speed and efficiency. This chapter will introduce the fundamental building blocks of the Q language, including its syntax, operators, and data types.

Basic Syntax

Q is a functional language, meaning it relies heavily on functions and expressions. It uses a concise syntax that is often described as terse but expressive.

• Comments:

  Code snippet

  // This is a single-line comment
  \c This is a multi-line comment

• Assignment:

  Code snippet

  x: 10 // Assign the value 10 to the variable x

• Functions:

  Code snippet

  f[x] := {x*2} // Define a function f that doubles its argument

• Control Flow:

  Code snippet

  [x>5; "greater than 5"; "less than or equal to 5"] // Conditional expression

Data Types

Q supports a rich set of data types, each optimized for performance.

• Atoms:

  • int: Integer (e.g., 1, -2, 0)

  • float: Floating-point number (e.g., 3.14, -0.5)

  • char: Character (e.g., a, Z)

  • symbol: Symbol (e.g., AAPL, IBM)

  Code snippet

  x: 10     // int
  y: 3.14   // float
  c: `a     // char
  s: `AAPL  // symbol

• Lists:

  • Ordered collection of items of the same type.

  Code snippet

  list1: 1 2 3 4
  list2: (`a`b`c)

• Dictionaries:

  • Unordered collection of key-value pairs.

  Code snippet

  dict1: (AAPL:100 IBM:200 GOOG:50)

• Tables:

  • Two-dimensional array with named columns.

  Code snippet

  table1:([] date:2023.01.01 2023.01.02; price:100 120)

Operators

Q provides a comprehensive set of operators for arithmetic, comparison, logical, and other operations.

• Arithmetic Operators:

  Code snippet

  + - * / %  // Addition, subtraction, multiplication, division, modulo

• Comparison Operators:

  Code snippet

  = <> < <= > >=  // Equal, not equal, less than, less than or equal, greater than, greater than or equal

• Logical Operators:

  Code snippet

  and or not  // Logical AND, OR, NOT

• Other Operators:

  Code snippet

  $  // Type cast
  #  // Count
  in  // Membership

Examples

Code snippet

// Create a list of numbers
numbers: 1 2 3 4 5

// Calculate the sum of the list
sum numbers

// Create a dictionary of stock prices
prices: (`AAPL:100 `GOOG:200 `IBM:150)

// Access the price of AAPL
prices[`AAPL]

// Create a simple table
trades: ([] time:10:00 10:01 10:02; price:101 102 99)

// Select rows where price is greater than 100
select from trades where price > 100

Summary

This chapter has introduced the fundamental building blocks of the Q language. By understanding these core concepts, you'll be well-prepared to explore more advanced features and applications of KDB+. In the following chapters, we will delve deeper into data manipulation, time series analysis, and other key areas of KDB+ development.

Note: This chapter provides a basic overview. KDB+ offers many more data types, operators, and functions than covered here. Refer to the official Kx documentation for a comprehensive list.