get-groups-of-entities.md

Get groups of entities

Sometimes instead of just listing entities, you want to group them into facets, and count how many entities are in each group. For example, maybe you want to count the number of Works by open access status. To do that, you call the entity endpoint, adding the group_by parameter. Example:

• Get counts of works by type:
  https://api.openalex.org/works?group_by=type

This returns a meta object with details about the query, and a group_by object with the groups you've asked for:

{
    meta: {
        count: 246136992,
        db_response_time_ms: 271,
        page: 1,
        per_page: 200,
        groups_count: 15
    },
    group_by: [
        {
            key: "article",
            key_display_name: "article",
            count: 202814957
        },
        {
            key: "book-chapter",
            key_display_name: "book-chapter",
            count: 21250659
        },
        {
            key: "dissertation",
            key_display_name: "dissertation",
            count: 6055973
        },
        {
            key: "book",
            key_display_name: "book",
            count: 5400871
        },
        ...
    ]
}

So from this we can see that the majority of works (202,814,957 of them) are type article, with another 21,250,659 book-chapter, and so forth.

You can group by most of the same properties that you can filter by, and you can combine grouping with filtering.

Group properties

Each group object in the group_by list contains three properties:

key

Value: a string; the OpenAlex ID or raw value of the group_by parameter for members of this group. See details on key and key_display_name.

key_display_name

Value: a string; the display_name or raw value of the group_by parameter for members of this group. See details on key and key_display_name.

count

Value: an integer; the number of entities in the group.

"Unknown" groups

The "unknown" group is hidden by default. If you want to include this group in the response, add :include_unknown after the group-by parameter.

• Group works by authorships.countries (unknown group hidden):
  https://api.openalex.org/works?group_by=authorships.countries
• Group works by authorships.countries (includes unknown group):
  https://api.openalex.org/works?group_by=authorships.countries:include_unknown

key and key_display_name

If the value being grouped by is an OpenAlex Entity, the key and key_display_name properties will be that Entity's id and display_name, respectively.

• Group Works by Institution:
  https://api.openalex.org/works?group_by=authorships.institutions.id
• For one group, key is "https://openalex.org/I136199984" and key_display_name is "Harvard University".

Otherwise, key is the same as key_display_name; both are the raw value of the group_by parameter for this group.

• Group Concepts by level:
  https://api.openalex.org/concepts?group_by=level
• For one group, both key and key_display_name are "3".

Group-by meta properties

meta.count is the total number of works (this will be all works if no filter is applied). meta.groups_count is the count of groups (in the current page).

If there are no groups in the response, meta.groups_count is null.

Due to a technical limitation, we can only report the number of groups in the current page, and not the total number of groups.

Paging

The maximum number of groups returned is 200. If you want to get more than 200 groups, you can use cursor pagination. This works the same as it does when getting lists of entities, so head over to the section on paging through lists of results to learn how.

Due to technical constraints, when paging, results are sorted by key, rather than by count.