---
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
canonical: "docs.dataddo.com/transformation-pipeline-stages"
---

> ## 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. |