REBOL 3 Functions: extract

extract series width /index pos /default value /into output

Extracts a value from a series at regular intervals.

Arguments:

series [series!]

width [integer!] - Size of each entry (the skip)

Refinements:

/index - Extract from an offset position

pos - The position(s) [number! logic! block!]

/default - Use a default value instead of none

value - The value to use (will be called each time if a function)

/into - Insert into a buffer instead (returns position after insert)

output [series!] - The buffer series (modified)

Description

Returns a series of values from regularly spaced positions within a specified series. For example:

data: ["Dog" 10 "Cat" 15 "Fish" 20]
probe extract data 2
["Dog" "Cat" "Fish"]

Essentially, extract lets you access a series as a record or "row" of a given length (specified by the width argument). The default, as shown above, extracts the first value. If you wanted to extract the second value (the second "column" of data):

data: ["Dog" 10 "Cat" 15 "Fish" 20]
probe extract/index data 2 2
[10 15 20]

In the example below, the width of each row is three:

people: [
    1 "Bob" "Smith"
    2 "Cat" "Walker"
    3 "Ted" "Jones"
]
block: extract people 3
probe block
[
 1
 2
 3
]

block: extract/index people 3 2
probe block
["Bob" "Cat" "Ted"]

Of course, extract works on any series, not just those that appear in a row format (such as that above). The example below creates a block containing every other word from a string:

str: "This is a given block here"
blk: parse str none
probe blk
["This" "is" "a" "given" "block" "here"]

probe extract blk 2
["This" "a" "block"]

probe extract/index blk 2 2
["is" "given" "here"]

Here is an example that uses extract to obtain the names of all the predefined REBOL/View VID styles:

probe extract system/view/vid/vid-styles 2