nwgrep

Grep your dataframes

Search and filter dataframes with grep-like patterns. Works with pandas, polars, and any backend supported by Narwhals.

At a Glance

# Find what you're looking for
df.grep("active")              # Simple search
df.grep("@gmail.com")          # Find patterns
df.grep(r"^\d{3}-\d{4}$")      # Regex support

Why nwgrep?

• 🔍 Familiar - grep-like interface for row-based dataframe filtering
• 🚀 Fast - Backend-agnostic, works with your preferred library
• 🎯 Simple - Three ways to use: function, pipe, or accessor
• ⚡ Efficient - Lazy evaluation with polars/daft for large datasets

Quick Start

uv add nwgrep

from nwgrep import nwgrep
import polars as pl

df = pl.DataFrame({
    "name": ["Alice", "Bob", "Eve"],
    "status": ["active", "locked", "active"],
})

# Find all rows containing "active"
result = nwgrep(df, "active")

# ┌───────┬────────┐
# │ name  ┆ status │
# │ ---   ┆ ---    │
# │ str   ┆ str    │
# ╞═══════╪════════╡
# │ Alice ┆ active │
# │ Eve   ┆ active │
# └───────┴────────┘

Three Ways to Use

Choose the style that fits your workflow:

1. Direct Function

from nwgrep import nwgrep
result = nwgrep(df, "active")

2. Pipe Method

result = (
    df
    .pipe(nwgrep, "active")
    .pipe(nwgrep, "@example.com", columns=["email"])
)

3. Accessor Method

For Polars and Pandas backends, you can use the accessor method to add .grep function directly to the DataFrame:

from nwgrep import register_grep_accessor
register_grep_accessor()

df.grep("active")                    # Search all columns
df.grep("ALICE", case_sensitive=False)  # Case-insensitive
df.grep("example.com", columns=["email"])  # Specific columns

Powerful Search Options

# Case-insensitive search
df.grep("ACTIVE", case_sensitive=False)

# Invert match (like grep -v)
df.grep("test", invert=True)

# Regex patterns
df.grep(r".*@example\.com", regex=True)

# Multiple patterns (OR logic)
df.grep(["Alice", "Bob"])

# Whole word matching
df.grep("active", whole_word=True)

# Column-specific search
df.grep("pattern", columns=["name", "email"])

# Highlight matching cells in notebooks (pandas/polars)
df.grep("error", highlight=True)  # Returns styled output with highlighted cells

Command Line Interface

Search parquet, feather, and other binary formats directly:

# Install cli
uv tool install "nwgrep[cli]"

# Basic search
nwgrep "error" logfile.parquet

# Case insensitive + regex
nwgrep -i -E "warn(ing)?" data.feather

# Column-specific search
nwgrep --columns email "@gmail.com" users.parquet

# Count matching rows
nwgrep --count "pattern" data.parquet

# List files with matches (like grep -l)
nwgrep -l "error" *.parquet

# Show only matching values (like grep -o)
nwgrep -o "error" data.parquet

# Stream as NDJSON (lazy evaluation)
nwgrep --format ndjson "pattern" huge_file.parquet

Backend Support

Works seamlessly with any dataframe library thanks to Narwhals:

Same code, any backend. Switch freely without rewriting your filters.

Installation

Basic installation:

uv add nwgrep
# or
pip install nwgrep

With specific backends:

uv add nwgrep             # core library
uv add nwgrep[cli]        # CLI for searching parquet/feather files using polars
uv add nwgrep[notebook]   # highlighting in notebooks (pandas/polars)
uv add nwgrep[all]        # include all features (cli + notebook)

Note: nwgrep is designed to be added to an existing environment with a dataframe library (pandas, polars, etc.) already installed. It does not install these backends by default, except for polars when installing the [cli] extra.

Features

• 🚀 Backend agnostic: Write once, run on any dataframe library
• 🔍 Multiple search modes: Literal, regex, case-sensitive/insensitive
• 📊 Column filtering: Search all columns or specific ones
• ⚡ Lazy evaluation: Efficient with large datasets (polars/daft)
• 🎯 Familiar interface: grep-like flags and behavior (-i, -v, -E)
• 🔧 Type safe: Full type hints with ty type checking
• 🎨 Flexible API: Function, pipe, or accessor - your choice
• 🖥️ CLI included: Search binary formats from the command line

Documentation

Full documentation available at erichutchins.github.io/nwgrep

• Installation Guide - Setup for all backends
• Usage Examples - Comprehensive examples
• API Reference - Complete function reference
• CLI Reference - Command-line usage

Quick Examples

Find Active Users

users = df.grep("active", columns=["status"])

Email Domain Search

gmail_users = df.grep("@gmail.com", columns=["email"])

Log Analysis

errors = df.grep(["ERROR", "CRITICAL"], columns=["level"])

Data Quality Checks

# Find rows without email addresses
missing_email = df.grep(r"\w+@\w+\.\w+", regex=True, invert=True)

Pipeline Filtering

result = (
    df
    .grep("active", columns=["status"])     # Active users
    .grep("@company.com", columns=["email"]) # Company emails
    .grep("admin", invert=True)              # Exclude admins
)

Narwhals Integration

nwgrep is a certified Narwhals plugin, enabling truly backend-agnostic code:

import narwhals as nw
from nwgrep import nwgrep

def process_any_dataframe(df_native):
    """Works with pandas, polars, pyarrow, or any Narwhals-supported backend"""
    df = nw.from_native(df_native)
    result = nwgrep(df, "pattern")
    return nw.to_native(result)

Contributing

Contributions welcome! See CONTRIBUTING.md for development setup and guidelines.

License

MIT License - see LICENSE file for details.

Built with Narwhals