llm-mr 0.1.0

Map-reduce spreadsheet operations powered by LLM prompts

llm-mr

llm-mr is a plugin for the llm command line tool that adds map/reduce/filter helpers for spreadsheet files. Use it when you have a large file you want to process with an LLM, and need to break it down into smaller chunks rather than processing the entire file at once.

The plugin supports CSV, JSONL, and XLSX input/output, and can be extended with third-party plugins for other formats.

Examples

Classify every row in a spreadsheet by sentiment:

llm mr map "Classify sentiment as positive/negative/neutral" -p -i feedback.csv -c sentiment -o out.csv

Summarize notes per department:

llm mr reduce "Summarize key themes" -p -i employees.csv --group-by department -o summary.csv

Filter a JSONL corpus to just the articles about a topic:

llm mr filter "about climate policy" -p -i articles.jsonl -o climate.jsonl

Pipe data through stdin/stdout — JSONL is the default streaming format:

cat data.jsonl | llm mr filter "about climate" -p | llm mr map "summarize" -c summary -p > out.jsonl

Expand each row into multiple output rows:

llm mr map "List the five largest cities" -p -i countries.csv --multiple -c city -o cities.csv

Bulk-rename columns with a Python expression — no LLM needed:

llm mr map 'row["name"].upper()' -e -i data.csv -c name_upper -o clean.csv

Or just describe what you want — interactive mode synthesizes the expression for you:

$ llm mr map "uppercase the names" -i data.csv -c name_upper -o clean.csv
Use deterministic expression?
  row["name"].upper() [Y/n]: Y
Using deterministic expression: row["name"].upper()

Installation

If you already have llm installed:

llm install llm-mr

New to llm? It's a command-line tool for interacting with language models. Install both together:

pip install llm llm-mr

Then configure a model and API key before continuing.

Writing I/O format plugins

Extra tabular formats (beyond CSV, JSONL, and XLSX) ship as normal Python packages that depend on llm-mr and register input and/or output plugins with pluggy via the llm_mr entry-point group.

Declare the entry point in pyproject.toml (the value is an importable module that is loaded for side effects; a package __init__.py works well):

[project.entry-points.llm_mr]
myformat = "llm_mr_myformat"

In that module, use mr_hookimpl from llm_mr.hookspecs and implement register_mr_inputs and/or register_mr_outputs. Each receives a register callback; pass an instance of your plugin class.

Plugins must satisfy the InputPlugin and/or OutputPlugin protocols in llm_mr.registries:

• Input: name (string id, e.g. "parquet"), extensions (e.g. [".parquet"]), and open(self, path: Path) as a context manager yielding a TableStream (rows iterable and optional fieldnames).
• Output: same name / extensions, plus write(self, path: Path, rows, fieldnames) that writes the file.

This is all that's required — stdin/stdout piping works automatically via a temp-file intermediary. For streaming without a temp file, also implement StreamableInput (open_stream(self, stream)) and/or StreamableOutput (write_stream(self, stream, rows, fieldnames)).

# llm_mr_myformat/__init__.py
from contextlib import contextmanager
from pathlib import Path
from typing import Iterator

from llm_mr.hookspecs import mr_hookimpl
from llm_mr.registries import TableStream


class ParquetInputPlugin:
    name = "parquet"
    extensions = [".parquet"]

    @contextmanager
    def open(self, path: Path) -> Iterator[TableStream]:
        rows = ...  # load rows as Iterable[Row]
        yield TableStream(rows=rows, fieldnames=[...])


@mr_hookimpl
def register_mr_inputs(register):
    register(ParquetInputPlugin())

After installation, llm mr discovers plugins through the same entry-point loading as the main llm tool; users install your package with pip / llm install like any other dependency.

Tutorial: Getting Started

Step 1: Install

Follow the Installation instructions above, then make sure you have a model configured. If you already use llm with an OpenAI or Anthropic key, you're all set — skip to Step 2.

If you'd rather use a free local model, Ollama is the quickest path:

llm install llm-ollama
ollama pull llama3.2:1b
llm -m llama3.2:1b "Hello, world!"

Step 2: Create Sample Data

Create foods.csv:

food,description
pizza,"Cheesy flatbread with tomato sauce and various toppings"
broccoli,"Green cruciferous vegetable, often steamed or roasted"
chocolate,"Sweet confection made from cocoa beans"
kale,"Dark leafy green vegetable, often used in salads"
ice_cream,"Frozen dairy dessert, sweet and creamy"

Step 3: Map

The map command adds a new column to the input file. Here we make a separate LLM request for each row to classify the food as a 'treat' or 'not treat'. The -p flag means "use my instruction as a literal prompt" — the text you provide is sent directly to the model for each row.

llm mr map \
  "Based on the food description, classify this as 'treat' or 'not treat'" \
  -p -i foods.csv -c tastiness -o foods_classified.csv

food,description,tastiness
pizza,"Cheesy flatbread with tomato sauce and various toppings",treat
broccoli,"Green cruciferous vegetable, often steamed or roasted",not treat
chocolate,"Sweet confection made from cocoa beans",treat
kale,"Dark leafy green vegetable, often used in salads",not treat
ice_cream,"Frozen dairy dessert, sweet and creamy",treat

Because we used the -p flag, the LLM is asked to classify each row with the exact prompt we supplied. Under the hood, the full prompt sent for the first row looks like this:

You are assisting with spreadsheet transformations.
<spreadsheet_rows>
<row_0>
{"food": "pizza", "description": "Cheesy flatbread with tomato sauce and various toppings"}
</row_0>
</spreadsheet_rows>
<user_instruction>
Based on the food description, classify this as 'treat' or 'not treat'
</user_instruction>
For each row, provide a single value for column 'tastiness' that answers the user_instruction.

Without the -p flag, you get interactive mode: the tool asks a planning model to figure out how to handle your instruction — either as a Python expression or as an LLM prompt. It shows you what it came up with and waits for you to press Y (accept) or n (reject) before anything runs.

In the example below, we reject the suggested Python expression and accept the generated LLM prompt instead:

$ llm mr map "label which foods are treats" -i foods.csv -c tastiness -o foods_classified.csv
Use deterministic expression?
  "treat" if any(w in row["description"].lower() for w in ("sweet", "dessert", "confection")) else "not treat" [Y/n]: n
Run as prompt per row?
  Based on the food name and description, classify this food as 'treat' or 'not treat'. Return only one of those two labels. [Y/n]: Y
Processing 5 batches (parallel=1)
  Completed batch 1/5
  ...
Wrote 5 rows to foods_classified.csv

Finally we can provide a Python expression directly with -e — no LLM call at all:

llm mr map '"sweet" in row["description"].lower()' -e -i foods.csv -c is_sweet -o sweets.csv

food,description,is_sweet
pizza,"Cheesy flatbread with tomato sauce and various toppings",False
broccoli,"Green cruciferous vegetable, often steamed or roasted",False
chocolate,"Sweet confection made from cocoa beans",True
kale,"Dark leafy green vegetable, often used in salads",False
ice_cream,"Frozen dairy dessert, sweet and creamy",True

Step 4: Filter (Expression)

You can use the filter command to keep only rows matching a criterion. Here we keep only the rows where the food is a 'treat'.

llm mr filter 'row["tastiness"] == "treat"' \
  -e -i foods_classified.csv -o treats_only.csv

food,description,tastiness
pizza,"Cheesy flatbread with tomato sauce and various toppings",treat
chocolate,"Sweet confection made from cocoa beans",treat
ice_cream,"Frozen dairy dessert, sweet and creamy",treat

Like the map step, we could have used the -p flag, or no flag for interactive mode.

Step 5: Reduce

The reduce command groups rows by a given column and summarizes each group. Output is a small table with two columns: the group key and the reduced value. By default those columns are named group and mr_result; here we rename them to match the grouping column and a clearer summary name using --group-key-column and -c / --column.

llm mr reduce "What characteristics do these foods share?" \
  -p -i foods_classified.csv --group-by tastiness \
  --group-key-column tastiness -c summary -o food_analysis.csv

tastiness,summary
treat,"These foods are typically sweet and have a high sugar content"
not treat,"These foods are typically green and have a bitter taste"

Again, we could have used -e to provide a Python expression directly (no LLM needed), or no flag for interactive mode.

Step 6: Expand with --multiple

Sometimes you want the model to produce several values per input row — for example, brainstorming related items or splitting a field into parts. The --multiple flag tells map to expect a list from each LLM call and expand each item into its own output row.

llm mr map "Come up with more foods matching this description" \
  -p -i food_analysis.csv --column food --multiple -o more_foods.csv

(Use the food_analysis.csv from step 5 so the input columns are tastiness and summary.)

tastiness,summary,food
treat,"These foods are typically sweet and have a high sugar content","cake"
treat,"These foods are typically sweet and have a high sugar content","candy_bar"
not treat,"These foods are typically green and have a bitter taste","spinach"
not treat,"These foods are typically green and have a bitter taste","swiss_chard"

Instruction Modes

llm mr has three commands: map to process each row, reduce to group rows, and filter to keep only rows matching a criterion.

Every command takes one positional argument — the instruction — plus a mode flag. Input is read from -i (file) or stdin; output goes to -o (file) or stdout.

Flag	Mode	What happens
(default)	Interactive	LLM tries to synthesize a Python expression; falls back to writing a prompt to run per-row if it can't. Asks you to confirm before running. Requires -i (cannot read from stdin).
-p	Prompt	Treat the instruction as a literal LLM prompt used to process each row.
-e	Expression	Treat the instruction as a Python expression evaluated locally. No LLM calls at all.

# Interactive — tool figures out the best execution strategy
llm mr map "uppercase the names" -i data.csv -c name_upper -o out.csv

# Prompt — send this exact prompt to the LLM for each row
llm mr map "Classify sentiment as positive/negative/neutral" -p -i data.csv -c sentiment -o out.csv

# Expression — Python expression, no LLM needed
llm mr map 'row["name"].upper()' -e -i data.csv -c name_upper -o out.csv

Selecting Models

To choose a different model from the llm tool's default for both the planning and per-item work, use the -m flag:

llm mr map "classify sentiment" -p -i data.csv -m gpt-4o -c sentiment -o out.csv

In interactive mode the planning step and per-item work can use different models. Either side can be overridden independently:

# Cheap worker, default planner
llm mr map "classify sentiment" -i data.csv --worker-model gpt-4o-mini -c sentiment -o out.csv

# Powerful planner, default worker
llm mr map "classify sentiment" -i data.csv --planning-model gpt-4o -c sentiment -o out.csv

# Override both
llm mr map "classify sentiment" -i data.csv --planning-model gpt-4o --worker-model gpt-4o-mini -c sentiment -o out.csv

In -p mode, only the worker model is used. In -e mode, no model is used.

Recovering from Failures

Both map and reduce write a sidecar error file (<output>.err) when batches or groups fail. Use --repair to retry only the failed items:

# Initial run — some batches may time out or fail
llm mr map "..." -p -i data.jsonl -c result -j 20 -o output.jsonl
# Warning: 3 batches failed; see output.jsonl.err — rerun with --repair

# Retry only the failed rows
llm mr map "..." -p -i data.jsonl -c result -j 4 -o output.jsonl --repair

The --repair flag is idempotent — if some retries still fail, they stay in the .err file. Delete the output and .err files to start fresh.

When output goes to stdout (no -o), error records are written as JSONL lines to stderr instead of a sidecar file. You can redirect them:

cat data.jsonl | llm mr map "..." -p 2>errors.jsonl > out.jsonl

--repair requires -o — it cannot be used with stdout output.

Python Expressions (-e)

Expression mode (-e) evaluates a single Python expression in a restricted sandbox — no imports, no file access, no side effects. This is a lightweight convenience restriction, not a security sandbox. A determined user can escape it. Do not rely on it to run untrusted expressions.

Map expressions

The expression receives a single variable row, a dict mapping column names to string values. It should return the value to store in the target column.

# row["name"] is available as a string
llm mr map 'row["name"].upper()' -e -i data.csv -c name_upper -o out.csv

# arithmetic on coerced values
llm mr map 'int(row["price"]) * 2' -e -i data.csv -c double_price -o out.csv

--multiple cannot be combined with -e.

Filter expressions

Same as map: the expression receives row (a dict). Return a truthy value to keep the row, falsy to discard it.

llm mr filter 'int(row["score"]) >= 10' -e -i data.csv -o filtered.csv
llm mr filter '"keyword" in row["text"].lower()' -e -i data.csv -o filtered.csv

Reduce expressions

The expression receives rows, a list of dicts (all rows in the current group). It should return a single aggregate value. Output columns are still group and mr_result by default (or whatever you pass with --group-key-column / -c).

llm mr reduce 'sum(int(r["score"]) for r in rows)' -e -i data.csv --group-by team -o totals.csv
llm mr reduce 'len(rows)' -e -i data.csv --group-by department -o counts.csv

Available builtins

All standard Python builtins are removed. Only the following are available:

len, int, float, str, bool, min, max, abs, round, sorted, list, tuple, set, dict, sum, any, all, enumerate, zip, map, filter

String methods (.upper(), .lower(), .split(), .strip(), .startswith(), etc.) and dict methods (.get(), .keys(), .values(), .items()) work normally since they are methods on the values, not builtins.

What is NOT allowed

• Imports — import, __import__(), and the full __builtins__ dict are all removed.
• Statements — the expression must be a single expression, not a statement. No =, for (except in comprehensions), if (except ternary), def, class, etc.
• I/O — open, print, input, and similar are unavailable.
• Arbitrary functions — only the builtins listed above are in scope.

Piping and Formats

All three commands support stdin/stdout piping alongside file-based I/O.

Input and output

• -i / --input — read from a file. Omit to read from stdin.
• -o / --output — write to a file. Omit to write to stdout.
• --in-place — (map only) overwrite the input file. Requires -i.

# File to file
llm mr filter "about climate" -p -i data.csv -o out.csv

# Pipe in, pipe out (JSONL default)
cat data.jsonl | llm mr filter "about climate" -p > out.jsonl

# Pipe chain
cat data.jsonl | llm mr filter "about climate" -p | llm mr map "summarize" -c summary -p > out.jsonl

# File in, pipe out (output matches input format)
llm mr map "summarize" -c summary -p -i data.csv > out.csv

When reading from stdin, interactive mode is not available — use -p or -e. If stdin is a TTY (nothing piped) and no -i is provided, the command errors with a helpful message.

Format detection

Format is detected automatically from file extensions. When piping (no file extension), JSONL is the default. Three flags give explicit control:

• -f / --format — set the default format for both directions
• --input-format — override input format only
• --output-format — override output format only

Resolution cascade (applied independently for input and output):

1. Specific flag (--input-format / --output-format)
2. File extension on -i / -o
3. General -f flag
4. Match the other end
5. JSONL fallback

# Pipe CSV explicitly
cat data.csv | llm mr filter "about climate" -p -f csv > out.csv

# CSV input file, JSONL stdout output
llm mr filter "about climate" -p -i data.csv --output-format jsonl

Status messages

All progress and status messages go to stderr, keeping stdout clean for data. This is true whether you use -o or pipe to stdout.

Non-interactive use (llm stdin)

When stdin is not a TTY (for example in CI or some automation tools), the underlying llm CLI may wait for input. If a command seems to hang, redirect stdin, e.g. append </dev/null to the command.

Command Reference

Map

Apply a transformation to each row, producing a new column.

llm mr map "Return a short summary of the notes" -p -i data.csv -c summary -o output.csv

Options:

• -i / --input — input file (omit to read stdin)
• -o / --output or --in-place — where to write results (omit -o for stdout)
• -c / --column — target column name (default: mr_result)
• -f / --format — default format for both directions
• --input-format / --output-format — override format per direction
• --where — pre-filter rows (e.g. status=active, score>=10)
• --few-shot N — use N existing values as examples
• --batch-size / --max-chars — control batching
• -j / --parallel — concurrent LLM calls (default: 1)
• --multiple — model emits a list per row; each item becomes its own output row
• -m / --model — LLM model to use
• --worker-model — model for per-item work (defaults to -m)
• --planning-model — model for interactive planning (defaults to -m)
• -n / --limit — only process first N rows
• --repair — retry failed rows from the .err sidecar (requires -o)
• --dry-run — show a sample prompt and exit without making LLM calls
• -v / --verbose — print each prompt as it is sent

Reduce

Group rows and summarize each group. Each output row has two fields: the group key (default column name group) and the reduced value (default mr_result). Use --group-key-column and -c to rename them.

llm mr reduce "Summarize performance" -p -i data.csv --group-by department -o summary.csv

With clearer column names:

llm mr reduce "Summarize performance" -p -i data.csv --group-by department \
  --group-key-column department -c summary -o summary.csv

With -e, you can aggregate with plain Python — no LLM needed:

llm mr reduce 'sum(int(r["score"]) for r in rows)' -e -i data.csv --group-by team -o totals.csv

Options:

• -i / --input — input file (omit to read stdin)
• -o / --output — output path (omit for stdout)
• --group-by — column(s) to group by (required, repeatable)
• --group-key-column — name of the group-key column in output (default: group)
• -c / --column — result column name (default: mr_result; must differ from --group-key-column)
• -f / --format — default format for both directions
• --input-format / --output-format — override format per direction
• --where — pre-filter rows
• --max-chars — max characters per reduction prompt
• -j / --parallel — concurrent groups
• -m / --model, --worker-model, --planning-model
• -n / --limit — only process first N groups
• --repair — retry failed groups (requires -o; use the same --group-key-column and -c as the original run)
• --dry-run — show a sample prompt and exit without making LLM calls
• -v / --verbose — print each prompt as it is sent

Filter

Keep only rows matching a criterion.

# Expression: Python filter, no LLM
llm mr filter 'int(row["score"]) >= 10' -e -i data.csv -o filtered.csv

# Prompt: LLM classifies each row
llm mr filter "about prediction markets" -p -i data.csv -m gpt-4o -o filtered.csv

# Interactive: tool tries to synthesize a filter expression
llm mr filter "articles from 2024" -i data.csv -o filtered.csv

# Pipe: stdin to stdout
cat data.jsonl | llm mr filter "about climate" -p > out.jsonl

Options:

• -i / --input — input file (omit to read stdin)
• -o / --output — output path (omit for stdout)
• -f / --format — default format for both directions
• --input-format / --output-format — override format per direction
• --where — pre-filter before instruction filter
• --batch-size / --max-chars — control batching for LLM mode
• -j / --parallel — concurrent batches
• -m / --model, --worker-model, --planning-model
• -n / --limit — only consider first N rows
• --dry-run — show a sample prompt and exit without making LLM calls
• -v / --verbose — print each prompt as it is sent

Debugging and Cost Tracking

Inspecting prompts

Use --dry-run to see the exact prompt and JSON schema that would be sent to the model, without actually making any API calls:

llm mr map "Classify sentiment" -p -i data.csv -c sentiment -o out.csv --dry-run

This prints the first batch's prompt, the schema, and the total number of batches that would be processed, then exits.

Use --verbose (or -v) to print every prompt as it is sent during a real run:

llm mr map "Classify sentiment" -p -i data.csv -c sentiment -o out.csv --verbose

Both flags work with map, reduce, and filter.

Cost tracking

The llm tool automatically logs every prompt and response to its SQLite database. After any llm mr run, you'll see a line like:

Made 47 LLM calls; run 'llm logs -n 47' to review

Use that command to inspect the prompts, responses, and token counts from your run. For more on the logs system, see the llm logs documentation.

Development

This project is managed with uv and just:

uv sync         # install dependencies
just test       # run tests
just lint       # check linting and formatting
just fix        # auto-fix linting and formatting
just check      # lint + test
just release    # check, tag v{version}, push branch + tag (see docs/release.md)

Release notes live in CHANGELOG.md; maintainers can follow docs/release.md for versioning, tags, and PyPI.

Future Work

• Rate-limiting for -j / --parallel — Currently -j 20 fires all requests concurrently with no throttling, which can trigger API rate limits (HTTP 429). Failed batches land in the .err sidecar and can be retried with --repair, but adding automatic retry with exponential backoff would make high-parallelism runs more robust.

• Token-limit awareness — The --max-chars flag uses character counts as a proxy for token limits. Actual token counts are model-specific and the llm library does not expose a tokenizer API, so precise per-model token budgeting is not feasible in the general case. The current heuristic (roughly 4 characters per token for English text) works in practice, and context-window errors are caught by the .err / --repair mechanism.

See Also

Some other tools offering "run an LLM prompt against every row" features with different trade-offs:

• smelt-ai — Python library that batch-processes list[dict] through LLMs with Pydantic-typed outputs, concurrency, and retry.
• Cellm — =PROMPT() formula for Excel.
• sheets-llm — =LLM() custom function for Google Sheets.
• Datablist — web app that runs ChatGPT prompts per CSV row.
• batch-llm.com — SaaS for uploading CSVs and running prompt templates per row via OpenAI, Anthropic, or Google models.