---
title: "Transformation Pipeline Stages"
slug: "transformation-pipeline-stages"
description: "Explore data transformation pipeline stages to streamline your workflow. Build robust data pipelines for seamless analytics and insights with Dataddo."
tags: ["Reference", "Data transformation"]
updated: 2023-11-07T11:57:25Z
published: 2023-11-07T11:57:25Z
---

> ## Documentation Index
> Fetch the complete documentation index at: https://docs.dataddo.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Transformation Pipeline Stages

On this page, you will find a comprehensive list of transformation pipeline [stages](/docs/transformation-pipeline-stages#transformation-pipeline-stages) and their [options](/docs/transformation-pipeline-stages#stages-options).

## Transformation Pipeline Stages
| Stage Name | Description |
|-----------------------|-------------------------|
| `$addFields`          | Adds new fields to documents. |
| `$bucket`             | Groups documents into specified buckets based on an expression and boundaries. [Options available](/docs/transformation-pipeline-stages#stages-options).|
| `$bucketAuto`         | Automatically distributes documents into a specified number of even buckets. [Options available](/docs/transformation-pipeline-stages#stages-options).|
| `$changeStream`       | Returns a Change Stream cursor; must be the first stage in the pipeline. |
| `$collStats`          | Provides statistics about a collection or view. |
| `$count`              | Counts the documents at this pipeline stage. |
| `$currentOp`          | Displays active and/or dormant operations. Requires the db.aggregate() method. [Options available](/docs/transformation-pipeline-stages#stages-options).|
| `$facet`              | Executes multiple aggregation pipelines in one stage, enabling multi-faceted aggregations. |
| `$geoNear`            | Orders documents based on geospatial proximity, incorporating $match, $sort, and $limit. [Options available](/docs/transformation-pipeline-stages#stages-options).|
| `$graphLookup`        | Conducts a recursive search, appending results to the output document as an array. [Options available](/docs/transformation-pipeline-stages#stages-options).|
| `$group`              | Groups documents by an expression, applying accumulator expressions to each group. |
| `$indexStats`         | Reports usage statistics for each index in the collection. |
| `$limit`              | Passes the first n documents unmodified to the pipeline. |
| `$listLocalSessions`  | Lists active sessions on the connected mongos or mongod instance. |
| `$listSessions`       | Lists sessions propagated to the system.sessions collection. |
| `$lookup`             | Performs a left outer join with another collection in the same database. [Options available](/docs/transformation-pipeline-stages#stages-options).|
| `$match`              | Filters documents, passing only matches to the next stage. |
| `$merge`              | Writes aggregation results to a collection; must be the last stage in the pipeline. [Options available](/docs/transformation-pipeline-stages#stages-options).|
| `$out`                | Writes aggregation results to a collection; must be the last stage. [Options available](/docs/transformation-pipeline-stages#stages-options).|
| `$planCacheStats`     | Provides plan cache data for a collection. |
| `$project`            | Reshapes each document, adding or removing fields. |
| `$redact`             | Reshapes documents based on their content, allowing field level redaction. |
| `$replaceRoot`        | Replaces a document with a specified embedded one, promoting the embedded document. |
| `$replaceWith`        | Alias for `$replaceRoot`. Replaces a document with a specified embedded one. |
| `$sample`             | Randomly selects a specified number of documents. [Options available](/docs/transformation-pipeline-stages#stages-options).|
| `$search`             | Executes a full-text search. |
| `$set`                | Alias for `$addFields`. Adds new fields to documents. |
| `$skip`               | Skips the first n documents, passing the rest unmodified. |
| `$sort`               | Reorders documents based on a specified sort key. |
| `$sortByCount`        | Groups documents by an expression's value and counts them. |
| `$unionWith`          | Combines results from two collections into one. [Options available](/docs/transformation-pipeline-stages#stages-options).|
| `$unset`              | Removes specified fields from documents. |
| `$unwind`             | Deconstructs an array field, outputting a document for each element. [Options available](/docs/transformation-pipeline-stages#stages-options).|

## Stages Options

| Stage | Option |
|---|---|
| `$bucket` | `groupBy`: An expression to group by. |
| | `boundaries`: An array specifying the boundaries to group documents. |
| | `default`: A literal that specifies the `_id` of an additional group for all documents that do not match any boundary. |
| `$bucketAuto` | `groupBy`: An expression to group by. |
| | `buckets`: The number of buckets to create. |
| `$currentOp` | `allUsers`: A boolean indicating if operations from all users should be returned. |
| | `localOps`: A boolean indicating if only operations on the local mongod instance should be returned. |
| `$geoNear` | `near`: The geospatial point to calculate distances from. |
| | `distanceField`: The field that will contain the calculated distance. |
| | `spherical`: A boolean specifying whether to treat the `near` point as a sphere. |
| | `maxDistance`: The maximum distance from the `near` point that the documents can be. |
| `$graphLookup` | `from`: The target collection for the recursive search. |
| | `startWith`: The expression that specifies the value of the `connectFromField` with which to start the recursive search. |
| | `connectFromField`: The field whose value `startWith` references. |
| | `connectToField`: The field in the documents of the `from` collection that is equal to the `connectFromField`. |
| | `as`: The array field added to each output document that contains the search results. |
| `$lookup` | `from`: The target collection. |
| | `localField`: The field from the input documents. |
| | `foreignField`: The field from the documents of the `from` collection. |
| | `as`: The name of the new array field to add to the input documents. |
| `$merge` | `into`: The target collection. |
| | `on`: The fields to match on. |
| | `whenMatched`: The action to take when a matching document exists. |
| | `whenNotMatched`: The action to take when no matching document exists. |
| `$out` | `collection`: The target collection. |
| `$sample` | `size`: The number of documents to randomly select. |
| `$unionWith` | `coll`: The name of the collection to union with. |
| | `pipeline`: An optional aggregation pipeline to apply to the specified collection before performing the union. |
| `$unwind` | `path`: The path to the array field to unwind. |
| | `includeArrayIndex`: The name of a new field to hold the array index of the element. |
| | `preserveNullAndEmptyArrays`: A boolean indicating whether to include as an output document those documents that have an empty array or missing array field. |