# innerJoin#

## Purpose#

Joins two matrices based upon user-specified key columns, with non-matching rows removed.

## Format#

C = innerJoin(A, ca, B, cb)#
Parameters:
• A (matrix) – matrix to join

• ca (scalar or vector) – key columns in A

• B (matrix) – matrix to join with A

• cb (scalar or vector) – key columns in B

Returns:

C (matrix) – result of join of A and B

## Examples#

### Basic usage#

```A = { 1 12 0.5,
3 15 0.6,
5 19 1.1,
2 11 0.9 };

B = { 7 0.3 5,
2 1.1 1,
9 0.1 3 };

/*
** Perform inner join on 'A' and 'B', based upon
** matches in column 1 of 'A' and column 3 of 'B'
*/
C = innerJoin(A, 1, B, 3);
```

After the code above, C equals:

```1 12 0.5 2 1.1
3 15 0.6 9 0.1
5 19 1.1 7 0.3
```

### Join on two columns#

```A = { 1 3.1 12 0.5,
3 1.2 15 0.6,
5 4.4 19 1.1,
2 6.9 11 0.9 };

B = { 7 20 0.3 5,
2 12 1.1 1,
9 15 0.1 3 };

a_keys = { 1, 3 };
b_keys = { 4, 2 };

/*
** Perform inner join on A and B, based on matches
** from the 1st column of A with the 4th column of B
** and the 3rd column of A with the 2nd column of B
*/
C = innerJoin(A, a_keys, B, b_keys);
```

After the code above, C equals:

```1 3.1 12 0.5 2 1.1
3 1.2 15 0.6 9 0.1
```

## Remarks#

The first columns of the output matrix C will be the columns of A in the same order as in A. The remaining columns of C will be the columns of B with the key columns removed.

Functions `outerJoin()`