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Vectors

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Christopher Ross-Gill edited this page Aug 1, 2016 · 1 revision

The vector! datatype is new in Rebol 3. The implementation described below takes effect in Alpha V22. Prior versions will not work.

Table of Contents

Definition

The vector datatype provides greater efficiency for numeric arrays.

A vector is a multidimensional array of a single numeric datatype (homogeneous). Vectors can be either integers of 8, 16, 32, or 64 bits, or decimals of 32 or 64 bits.

The benefit of a vector is the memory it saves. For example, if you need to index a large file and keep track of 100000 index positions, a vector will be four times more memory efficient than using a block, saving about 1.2MB in this case.

Making A Vector

There are two general formats for making a new vector: 

v1: make vector! 100000
v1: make vector! [decimal! 32 100000]

The first is a simple shortcut that makes a vector of the default type: 32 bit signed integer of one dimension.

The second format can be used to create a variety of vectors, depending on your requirements.

The general syntax is 

make vector! [sign type bits size]

or: 

make vector! [sign type bits [size1 size2 size3 ...]] ; not yet supported

where:

  • sign (optional) - '-' for signed (default) or '+' for unsigned
  • type (optional) - integer! (default) or decimal! (floating point) type
  • bits - number of bits (32 is the default)
  • size - size of the vector
And, instead of size, you can provide a block of sizes for each dimension of the vector.

Integer values can be 8, 16, 32, and 64 bits.

Decimal values can be 32 or 64 bits.

Examples of Make

Vector of 1000 signed 16 bit integers: 

make vector! [16 1000]

Vector of 500 signed 64 bit decimals: 

make vector! [decimal! 64 500]

Vector of 2000 unsigned 32 bit integers: 

make vector! [+ 32 2000]

Vector of 10000 unsigned 8 bit integers: 

make vector! [+ 8 2000]

Two dimensional vector of signed 64 bit integers: 

make vector! [64 [200 1000]]  ; Note: not in current alpha release.

Access to Vector Elements

Just like other series you can access elements of a vector with a path.

However, unlike other series, we have made vectors zero-based. We did this as a test, to see if it makes more sense, because vectors are more like arrays found in C and other languages. Let us know what you think of this change.

So as a simple example, to set and print the first element: 

v: make vector! 100
v/0: 1234567
print v/0

Or, as a 16 bit integer value, it's mostly the same: 

v: make vector! [16 100]
v/0: 1234
print v/0

Or, as a 32 bit decimal value: 

v: make vector! [decimal! 32 100]
v/0: 123.45
print v/0

Note the rounding error that come from the internal floating point math, so be sure to keep that in mind.

You can also use PICK and POKE functions: 

poke v 9 100
print pick v 9
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