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# uniqArrayIf

> Example of using the uniqArrayIf combinator

<h2 id="description">
  Description
</h2>

The [`Array`](/reference/functions/aggregate-functions/combinators#-array) and [`If`](/reference/functions/aggregate-functions/combinators#-if) combinators can be applied to the [`uniq`](/reference/functions/aggregate-functions/uniq)
function to count the number of unique values in arrays for rows where the
condition is true, using the `uniqArrayIf` aggregate combinator function.

<Note>
  -`If` and -`Array` can be combined. However, `Array` must come first, then `If`.
</Note>

This is useful when you want to count unique elements in an array based on
specific conditions without having to use `arrayJoin`.

<h2 id="example-usage">
  Example usage
</h2>

<h3 id="count-unique-products">
  Count unique products viewed by segment type and engagement level
</h3>

In this example, we'll use a table with user shopping session data to count the
number of unique products viewed by users of a specific user segment and with
an engagement metric of time spent in the session.

```sql title="Query" theme={null}
CREATE TABLE user_shopping_sessions
(
    session_date Date,
    user_segment String,
    viewed_products Array(String),
    session_duration_minutes Int32
) ENGINE = Memory;

INSERT INTO user_shopping_sessions VALUES
    ('2024-01-01', 'new_customer', ['smartphone_x', 'headphones_y', 'smartphone_x'], 12),
    ('2024-01-01', 'returning', ['laptop_z', 'smartphone_x', 'tablet_a'], 25),
    ('2024-01-01', 'new_customer', ['smartwatch_b', 'headphones_y', 'fitness_tracker'], 8),
    ('2024-01-02', 'returning', ['laptop_z', 'external_drive', 'laptop_z'], 30),
    ('2024-01-02', 'new_customer', ['tablet_a', 'keyboard_c', 'tablet_a'], 15),
    ('2024-01-02', 'premium', ['smartphone_x', 'smartwatch_b', 'headphones_y'], 22);

-- Count unique products viewed by segment type and engagement level
SELECT 
    session_date,
    -- Count unique products viewed in long sessions by new customers
    uniqArrayIf(viewed_products, user_segment = 'new_customer' AND session_duration_minutes > 10) AS new_customer_engaged_products,
    -- Count unique products viewed by returning customers
    uniqArrayIf(viewed_products, user_segment = 'returning') AS returning_customer_products,
    -- Count unique products viewed across all sessions
    uniqArray(viewed_products) AS total_unique_products
FROM user_shopping_sessions
GROUP BY session_date
ORDER BY session_date
FORMAT Vertical;
```

```response title="Response" theme={null}
Row 1:
──────
session_date:                2024-01-01
new_customer⋯ed_products:    2
returning_customer_products: 3
total_unique_products:       6

Row 2:
──────
session_date:                2024-01-02
new_customer⋯ed_products:    2
returning_customer_products: 2
total_unique_products:       7
```

<h2 id="see-also">
  See also
</h2>

* [`uniq`](/reference/functions/aggregate-functions/uniq)
* [`Array combinator`](/reference/functions/aggregate-functions/combinators#-array)
* [`If combinator`](/reference/functions/aggregate-functions/combinators#-if)