# Arrays

Create and manipulate arrays.

An array is a creature from the early days of computing when everything was binary and the first counting number was zero so a three by three array (two dimensions) would be set up as

`MAKE “A ARRAY [3 3]`

which would sensibly numbered [1 1] through [3 3] but in fact the cells in the array are actually numbered as:

```[0 0][0 1][0 2]
[1 0][1 1][1 2]
[2 0][2 1][2 2]```

You would put “X” into the middle cell by `ASET :A [1 1] “X` (rather than the logical `ASET :A [2 2] “X`) which would result in…

```[   ][   ][   ]
[   ][ X ][   ]
[   ][   ][   ]```

Then someone would put “O” into the lower right cell by `ASET :A [2 2] “O` (rather than the equally logical `ASET :A [3 3] “O`) which would result in:

```[   ][   ][   ]
[   ][ X ][   ]
[   ][   ][ O ]```

…and so on. If an element has not been defined yet, it contains an empty list.

If you prefer to start array indexing from 1 on, you can change the `"PREFS` property `ARRAYBASE` to the value 1 (or any other value that you prefer as the lowest index). This settings also affects grids.

Access to elements of an array is much faster than access to elements of a list, because the location in the array can be pre-computed instead of having to walk through the list.

## AGET

Reports the value of an array element.

#### Syntax

```AGET array number
AGET array list```

#### Description

AGET reports the value in a specific location of an array as specified by its inputs. The first element of input is the array to be accessed, while the second element specifies the array element to be obtained. For one-dimensional arrays, the second element may be a number starting from 0; for multi-dimensional arrays, the input element is a list of numbers, where each number stands for one dimension. If no value is stored, arrays report an empty list [].

See also `ARRAYDIMS`, `ARRAY`, `FILLARRAY`, and `ASET`.

#### Example

```MAKE "A ARRAY [2 2]
AGET :A [1 0]
Result: []
ASET :A [1 1] [SQUARE 4]
AGET :A [1 1]
Result: [SQUARE 4]
```

## ARRAY

Creates an array.

#### Syntax

```ARRAY number
ARRAY list
ARRAY word
(ARRAY number list)
(ARRAY list list)```

#### Description

ARRAY creates an array of the size specified by its input. If the input is a number, a one-dimensional array of the specified size is created. Its elements may be accessed by numbers between 0 and the input size less 1.

If the input to ARRAY is a list, the list describes the array. Each number in the list corresponds to the size of one dimension of the array. In order to access an element of a multi-dimensional array, a list of numbers must be supplied to the `AGET` and `ASET` primitives, where each number must be in the range from 0 to the number supplied for the corresponding dimension less 1.

If the input is a word, ARRAY creates a one-dimensional array and fills the array with each character of that word.

A list may be supplied as an optional second element if ARRAY and all its arguments are enclosed in parentheses. The contents of this list are the initial values of the array elements. For a description of the structure of the list, see `FILLARRAY`.

See also `ARRAYDIMS`, `FILLARRAY`, and `LISTARRAY`.

#### Example

```MAKE "A ARRAY [2 2]
ASET :A [1 0] [HELLO WORLD]
AGET :A [1 0]
Result: [HELLO WORLD]
AGET :A [0 0]
Result: []
```

## ARRAY? (ARRAYP)

Reports TRUE if the object is an array.

#### Syntax

`ARRAY? object`

#### Description

ARRAY? reports TRUE if its input is an array, and FALSE otherwise.

#### Example

```MAKE "A ARRAY 2
ARRAY? :A
Result: TRUE
```

## ARRAYDIMS

Reports the structure of an array.

#### Syntax

`ARRAYDIMS array`

#### Description

ARRAYDIMS reports a list of numbers describing the dimensions of the array named in its input. This list matches the input to the `ARRAY` command when the array was created. If the array has not been dimensioned yet because it has been created with the `NEW` command, ARRAYDIMS reports the empty list.

See also `ARRAY` and `FILLARRAY`.

#### Example

```MAKE "A ARRAY [2 2]
ARRAYDIMS :A
Result: [2 2]
```

## ASET

Sets the value of an array element.

#### Syntax

```ASET array number value
ASET array list value```

#### Description

ASET stores a value into a specific element of an array. ASET requires three inputs: the first input is the name of the array, the second input describes the array element where the value is to be stored, and the third input is the value itself. For one-dimensional arrays, the second input must be a number. For multi-dimensional arrays, the second input is a list of numbers, where each number stands for one dimension.

See also `ARRAYDIMS`, `ARRAY`, `FILLARRAY`, and `AGET`.

#### Example

```MAKE "A ARRAY [2 2]
ASET :A [1 0] [HELLO WORLD]
AGET :A [1 0]
Result: [HELLO WORLD]
AGET :A [0 0]
Result: []
```

## FILLARRAY

Sets the values of an array.

#### Syntax

`FILLARRAY array list or word`

#### Description

FILLARRAY initializes the array named in its first input with the data in the list given as its second input. If the list is non-structured, the array is filled sequentially regardless of its dimensions. If the list is structured, the array is filled according to the structure of the list and its dimensions.

If the input is a word, FILLARRAY initializes the array with each character of the word.

See also `ARRAY`, `AGET`, `ASET`, and `AGET`.

#### Example

```MAKE "A ARRAY [2 2]
FILLARRAY :A [1 2 3 4]
LISTARRAY :A
Result: [[1 2][3 4]]
```

## LISTARRAY

Reports the values of an array as a list.

#### Syntax

`LISTARRAY array`

#### Description

LISTARRAY reports a list whose structure resembles the dimensional structure of the array named in its input.

See also `ARRAY`, `AGET`, `ASET`, and `FILLARRAY`.

#### Example

```MAKE "A ARRAY [2 2]
ASET :A [0 1] 25
ASET :A [1 1] 50
LISTARRAY :A
Result: [[[] 25][[] 50]]
```

## SETARRAYDIMS

Sets the structure of an array.

#### Syntax

```SETARRAYDIMS array word
SETARRAYDIMS array list```

#### Description

SETARRAYDIMS accepts a number or a list of numbers describing the dimensions of the array named in its first input. It sets up the structure of the array as requested. All data is released, and the array is empty afterwards.

See also `ARRAY`, `ARRAYDIMS`, and `FILLARRAY`.

#### Example

```MAKE "A ARRAY [2 2]
SETARRAYDIMS :A [3 3]
ARRAYDIMS :A
```

## TEXTARRAY

Sets the structure of an array.

#### Syntax

`TEXTARRAY array`

#### Description

TEXTARRAY converts the contents of an array into a Logo word. The array must only have a single dimension. If an element is a number, TEXTARRAY treats the number as a Unicode character code. The array elements are concatenated without spaces between them.

See also `ARRAY`, `ARRAYDIMS`, and `FILLARRAY`.

#### Example

```MAKE "A { H E LLO 32 20013 22269}
TEXTARRAY :A
Result: HELLO 中国
```