kdb+ Q中列表值更新、存在性检查及学习资源问询

Let's break down each of your requirements step by step, with working Q code and clear explanations:

1. Update elements by adding their index #

Your initial attempts with a+?[] and a+a[] didn't work because ? generates random numbers, and a[] just references the list's elements (not their positions). In Q, indices start at 0—you can generate a list of matching indices using til count a (which creates a sequence from 0 to the length of a minus 1), then perform element-wise addition with the original list:

a: (1;2;3;4;5)
a: a + til count a  / Result: (1;3;5;7;9)

Q automatically handles element-wise arithmetic for lists of the same length, so this updates each value correctly.

2. Check if numbers 2, 3, 4 exist in the list #

Use the in operator to check membership—it returns a boolean list showing which target values are present:

(2;3;4) in a  / Result: (1b;1b;1b) (all three exist in the original list)

If you want to verify that all three numbers are present in one check, wrap the result with all:

all (2;3;4) in a  / Result: 1b (true)

3. Count the number of odd elements #

Odd numbers leave a remainder of 1 when divided by 2. You can use mod to calculate this, then sum the resulting values (since 1b/1 represents odd, 0b/0 represents even):

sum a mod 2  / Result: 3 (original list has 1, 3, 5 as odd numbers)

For more explicit readability, you could also write:

sum 1 = 2 mod a  / Same result as above

Recommended Q Learning Resources #

Here are some high-quality, trusted resources to master Q:

• Q For Mortals: The de facto beginner-friendly guide to Q, written by kdb+ experts. It covers core syntax, data structures, and practical use cases in depth.
• Official kdb+ Documentation: The official code.kx docs include step-by-step tutorials, Q-SQL guides, and full reference materials for all kdb+ features.
• Q Programming (Book): A comprehensive resource that dives into advanced Q techniques, performance optimization, and real-world data processing.
• kdb+ Community Forums: Engage with experienced Q developers, ask targeted questions, and learn from shared solutions—this is a great place to troubleshoot and expand your knowledge.
• Official kdb+ Video Tutorials: Short, focused videos from kx that walk through key concepts and hands-on scenarios for both beginners and advanced users.

内容的提问来源于stack exchange，提问作者culldog88