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VECTOR_NUM_ELEMENTS

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The VECTOR_NUM_ELEMENTS function returns the number of elements in the vector.

Syntax

VECTOR_NUM_ELEMENTS(vector_expression)

Arguments

  • vector_expression: An expression that evaluates to a vector. Vectors can be stored in SingleStore using the BLOB type (BLOB Types).

Return Type

Returns a 64-bit Integer or NULL.

Remarks

If the input is NULL, NULL will be returned.

Using VECTOR_NUM_ELEMENTS with Vectors as BLOBs

The following examples and descriptions show the use of VECTOR_NUM_ELEMENTS with an argument that is a vector stored as a BLOB.

Example 1 - BLOB Argument

Create a table with a column of type BLOB to store the vectors. The second column in this table, with column name vec and type BLOB, will store the vectors. This example demonstrates storing vector data using BLOBs, hence the column of type BLOB named vec.

Then use the JSON_ARRAY_PACK built-in function to easily insert properly formatted vectors.

CREATE TABLE vectors_b (id int, vec BLOB not null);


INSERT INTO vectors_b VALUES (1, JSON_ARRAY_PACK('[0.1, 0.8, 0.2, 0.555]')); 
INSERT INTO vectors_b VALUES (2, JSON_ARRAY_PACK('[0.45, 0.55, 0.495, 0.5]'));

The following query counts the number of elements of the vectors in the vectors_b table.

SELECT id, VECTOR_NUM_ELEMENTS(vec)
FROM vectors_b
ORDER BY id;
+------+--------------------------+
| id   | VECTOR_NUM_ELEMENTS(vec) |
+------+--------------------------+
|    1 |                        4 |
|    2 |                        4 |
+------+--------------------------+

Using Suffixes for Other Element Types with BLOBs

The default element type for vector storage and processing is 32-bit floating point (F32). However, other element types are supported.

You can specify the datatype of the vector elements to be used in the operation by adding a suffix to the function. All operations are done using the specified datatype. Omitting the suffix from the function is equivalent to suffixing it with _F32.

When using a suffix, the return type will be the type of the suffix.

The following table lists the suffixes and their data type.

Suffix

Data Type

_I8

8-bit signed integer

_I16

16-bit signed integer

_I32

32-bit signed integer

_I64

64-bit signed integer

_F32

32-bit floating-point number (IEEE standard format)

_F64

64-bit floating-point number (IEEE standard format)

Example 2 - BLOBs with 16-bit Integers

Below is an example of using JSON_ARRAY_PACK and VECTOR_NUM_ELEMENTS with 16-bit signed integers.

First create a table of vectors stored as 16-bit integers. Note the use of the _I16 suffix on JSON_ARRAY_PACK.

CREATE TABLE vectors_b_i (id int, vec BLOB not null);


INSERT INTO vectors_b_i VALUES (1, JSON_ARRAY_PACK_I16('[1, 3, 2, 5]')); 
INSERT INTO vectors_b_i VALUES(2, JSON_ARRAY_PACK_I16('[23, 4, 1, 8]'));

The following query counts the number of elements in the vectors in the vectors_b_i table.

SELECT id, VECTOR_NUM_ELEMENTS_I16(vec)
FROM vectors_b_i
ORDER BY id;
+------+------------------------------+
| id   | VECTOR_NUM_ELEMENTS_I16(vec) |
+------+------------------------------+
|    1 |                            4 |
|    2 |                            4 |
+------+------------------------------+

Note

Be sure that the suffixes you use to pack the vector data match the suffixes you use to unpack the data and the suffixes you use on functions to process that data.

Formatting Binary Vector Data for BLOBs

When using the BLOB type for vector operations, vector data can be formatted using JSON_ARRAY_PACK. If your vector data is already in a packed binary format, you can load that data into the BLOBs. The data must be encoded as a BLOB containing packed numbers in little-endian byte order. Vectors stored as BLOBs can be of any length; however, the input blob length must be divisible by the size of the packed vector elements (1, 2, 4 , or 8 bytes, depending on the vector element).

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Last modified: May 30, 2024

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