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$min (Accumulator Operator)

Definition

$min

Returns the minimum value across a group of documents.

The $min accumulator is available in these stages:

Note

Disambiguation

This page describes $min when used as an accumulator. Accumulators return an aggregated value like sum, maximum, or minimum across a group of input documents.

You can also use $min in these other contexts:

$min (expression), which returns the minimum value from an array.
$min (window function), which is used in the $setWindowFields stage to return the minimum value from documents in a particular window.

Syntax

{ $min: <expression> }

Behavior

Result Type

When $min compares values of different types, it uses the BSON comparison order to determine which value is smaller.

Null or Missing Values

If some documents have a null value for the field or are missing the field, $min ignores them. It considers only the non-null and non-missing values.

If all documents have a null value for the field or are missing the field, $min returns null.

Array Operand

In the $group stage, if the expression resolves to an array, $min does not traverse the array. It compares the array as a whole.

Equal Values

If multiple values compare as equal, $min may return any of those values. There is no guarantee which equal value $min returns.

For example, under a case-insensitive collation, "a" and "A" can compare as equal. There is no guarantee which will be returned.

Example

The examples on this page use data from the sample_mflix dataset. For details on how to load this dataset into your self-managed MongoDB deployment, see Load the Sample Dataset. If you made any modifications to the sample databases, you may need to drop and recreate the databases to run the examples on this page.

Use $min in a $group Stage

The following example groups movies by MPAA rating and returns the lowest IMDb rating for each group.

db.movies.aggregate( [
   {
      $match: {
         rated: { $in: [ "G", "PG", "PG-13", "R" ] },
         "imdb.rating": { $type: "double" }
      }
   },
   {
      $group: {
         _id: "$rated",
         lowestRating: { $min: "$imdb.rating" }
      }
   },
   {
      $sort: { _id: 1 }
   }
] )

[
  { _id: 'G', lowestRating: 1.6 },
  { _id: 'PG', lowestRating: 1.6 },
  { _id: 'PG-13', lowestRating: 1.9 },
  { _id: 'R', lowestRating: 2 }
]

The preceding pipeline:

Uses $match to filter for movies with a rated value of G, PG, PG-13, or R and a numeric IMDb rating.
Uses $group to group movies by the rated field and computes lowestRating using $min on imdb.rating.
Uses $sort to return the results in alphabetical order by content rating.

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