core_concepts

Expressions are the foundation of Polars' API. They are composable units that describe data transformations without executing them immediately.

Skills
Scientific
1

What it does and how to use it

A skill that teaches Claude Code to do scientific tasks well. It is packaged knowledge the model uses whenever it is relevant.

Install the skill (command above).
In Claude Code, describe what you need - the skill turns on by itself when the context fits.
No commands to memorize: you talk in plain language and the skill does the rest.

Install (Claude Code)

mkdir -p .claude/skills/core-concepts-9 && curl -fsSL https://doutorai.pt/data/lib/skills__core-concepts-9.md -o .claude/skills/core-concepts-9/SKILL.md

Paste this command into the terminal, in your project folder, and the component installs automatically.

Content

# Polars Core Concepts

## Expressions

Expressions are the foundation of Polars' API. They are composable units that describe data transformations without executing them immediately.

### What are Expressions?

An expression describes a transformation on data. It only materializes (executes) within specific contexts:
- `select()` - Select and transform columns
- `with_columns()` - Add or modify columns
- `filter()` - Filter rows
- `group_by().agg()` - Aggregate data

### Expression Syntax

**Basic column reference:**
```python
pl.col("column_name")
```

**Computed expressions:**
```python
# A

- 🔒 Full content on the Pro plan (€7.99/month) -

Need help with Claude Code?

Ask Dr AI - it explains things simply.

Need a tailor-made solution?

Not sure where to start with AI in your business? Get a free assessment and a tailored plan - no commitment.

Save hours every week with AI, no hassle

Doutor AI gives you 1,859 ready-to-copy AI prompts, by industry and in plain English - plus a complete technical library for those who want to go further.

See plans