@stdlib/slice-base-seq2slice
v0.2.2
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Convert a subsequence string to a Slice object.
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seq2slice
Convert a subsequence string to a
Slice
object.
Installation
npm install @stdlib/slice-base-seq2slice
Usage
var seq2slice = require( '@stdlib/slice-base-seq2slice' );
seq2slice( str, len, strict )
Converts a subsequence string to a Slice
object, where len
specifies the maximum number of elements allowed in the slice.
var s = seq2slice( ':5', 10, false );
// returns <Slice>
var v = s.start;
// returns 0
v = s.stop;
// returns 5
v = s.step;
// returns 1
A subsequence string has the following format:
<start>:<stop>:<increment>
where
- If an
increment
is not specified, the default increment is1
. An increment of zero is not allowed. - The
start
index is inclusive. - The
stop
index is exclusive. - Both
start
andstop
indices are optional. If not provided,start
andstop
default to index extremes. Which extremes correspond to which index depends on whether theincrement
is positive or negative. - Both
start
andstop
can be negative; in which case, the corresponding index is resolved by subtracting the respective value from the provided lengthlen
. - Both
start
andstop
can use theend
keyword (e.g.,end-2::2
,end-3:
, etc), which supports basic subtraction and division. - The
end
keyword resolves to the provided lengthlen
. Thus,:-1
is equivalent to:end-1
,:-2
is equivalent to:end-2
, and so on and so forth. The exception is when performing a division operation when theincrement
is less than zero; in which case,end
is equal tolen-1
in order to preserve user expectations whenend/d
equals a whole number and slicing from right-to-left. The result from a division operation is rounded down to the nearest integer value.
var s = seq2slice( 'end:2:-1', 10, false );
// returns <Slice>
var v = s.start;
// returns 9
v = s.stop;
// returns 2
v = s.step;
// returns -1
s = seq2slice( 'end-2:2:-1', 10, false );
// returns <Slice>
v = s.start;
// returns 8
v = s.stop;
// returns 2
v = s.step;
// returns -1
s = seq2slice( 'end/2:2:-1', 10, false );
// returns <Slice>
v = s.start;
// returns 4
v = s.stop;
// returns 2
v = s.step;
// returns -1
The function returns an error object if provided an invalid subsequence string.
var s = seq2slice( '1:2:3:4', 10, false );
// returns { 'code': 'ERR_SLICE_INVALID_SUBSEQUENCE' }
When strict
is true
, the function returns an error object if a subsequence string resolves to a slice exceeding index bounds.
var s = seq2slice( '10:20', 10, true );
// returns { 'code': 'ERR_SLICE_OUT_OF_BOUNDS' }
A returned error object may have one of the following error codes:
- ERR_SLICE_INVALID_SUBSEQUENCE: a subsequence string is invalid.
- ERR_SLICE_INVALID_INCREMENT: a subsequence string must have a non-zero increment.
- ERR_SLICE_OUT_OF_BOUNDS: a subsequence string resolves to a slice exceeding index bounds.
Notes
- When
len
is zero, the function always returns a Slice object equivalent to0:0:<increment>
. - When
strict
isfalse
, the resolved slice start is clamped to the slice index bounds (i.e.,[0, len)
). - When
strict
isfalse
, the resolved slice end is upper bound clamped tolen
(i.e., one greater than the last possible index). - When the increment is negative, the resolved slice end value may be
null
, thus indicating that a non-empty slice should include the first index. - The function ensures that results satisfy the convention that
:n
combined withn:
is equivalent to:
(i.e., selecting all elements). This convention matches Python slice semantics, but diverges from the MATLAB convention where:n
andn:
overlap by one element. - Unlike MATLAB, but like Python, the subsequence string is upper-bound exclusive. For example, in Python,
0:2
corresponds to the sequence{0,1}
. In MATLAB,1:3
corresponds to{1,2,3}
.
Examples
var seq2slice = require( '@stdlib/slice-base-seq2slice' );
var s = seq2slice( ':', 5, false );
console.log( 'start: %s. stop: %s. step: %s.', s.start, s.stop, s.step );
// => 'start: 0. stop: 5. step: 1.'
s = seq2slice( '2:', 5, false );
console.log( 'start: %s. stop: %s. step: %s.', s.start, s.stop, s.step );
// => 'start: 2. stop: 5. step: 1.'
s = seq2slice( ':3', 5, false );
console.log( 'start: %s. stop: %s. step: %s.', s.start, s.stop, s.step );
// => 'start: 0. stop: 3. step: 1.'
s = seq2slice( '2:4', 5, false );
console.log( 'start: %s. stop: %s. step: %s.', s.start, s.stop, s.step );
// => 'start: 2. stop: 4. step: 1.'
s = seq2slice( '1:4:2', 5, false );
console.log( 'start: %s. stop: %s. step: %s.', s.start, s.stop, s.step );
// => 'start: 1. stop: 4. step: 2.'
s = seq2slice( '2::2', 5, false );
console.log( 'start: %s. stop: %s. step: %s.', s.start, s.stop, s.step );
// => 'start: 2. stop: 5. step: 2.'
s = seq2slice( ':-2', 5, false );
console.log( 'start: %s. stop: %s. step: %s.', s.start, s.stop, s.step );
// => 'start: 0. stop: 3. step: 1.'
s = seq2slice( ':-1:2', 5, false );
console.log( 'start: %s. stop: %s. step: %s.', s.start, s.stop, s.step );
// => 'start: 0. stop: 4. step: 2.'
s = seq2slice( '-4:-1:2', 5, false );
console.log( 'start: %s. stop: %s. step: %s.', s.start, s.stop, s.step );
// => 'start: 1. stop: 4. step: 2.'
s = seq2slice( '-5:-1', 5, false );
console.log( 'start: %s. stop: %s. step: %s.', s.start, s.stop, s.step );
// => 'start: 0. stop: 4. step: 1.'
s = seq2slice( '::-1', 5, false );
console.log( 'start: %s. stop: %s. step: %s.', s.start, s.stop, s.step );
// => 'start: 4. stop: null. step: -1.'
s = seq2slice( ':0:-1', 5, false );
console.log( 'start: %s. stop: %s. step: %s.', s.start, s.stop, s.step );
// => 'start: 4. stop: 0. step: -1.'
s = seq2slice( '3:0:-1', 5, false );
console.log( 'start: %s. stop: %s. step: %s.', s.start, s.stop, s.step );
// => 'start: 3. stop: 0. step: -1.'
s = seq2slice( '-1:-4:-2', 5, false );
console.log( 'start: %s. stop: %s. step: %s.', s.start, s.stop, s.step );
// => 'start: 4. stop: 1. step: -2.'
s = seq2slice( ':end', 5, false );
console.log( 'start: %s. stop: %s. step: %s.', s.start, s.stop, s.step );
// => 'start: 0. stop: 5. step: 1.'
s = seq2slice( ':end-1', 5, false );
console.log( 'start: %s. stop: %s. step: %s.', s.start, s.stop, s.step );
// => 'start: 0. stop: 4. step: 1.'
s = seq2slice( ':end/2', 5, false );
console.log( 'start: %s. stop: %s. step: %s.', s.start, s.stop, s.step );
// => 'start: 0. stop: 2. step: 1.'
s = seq2slice( 'end/2::-1', 5, false );
console.log( 'start: %s. stop: %s. step: %s.', s.start, s.stop, s.step );
// => 'start: 2. stop: null. step: -1.'
s = seq2slice( 'end-2::-1', 5, false );
console.log( 'start: %s. stop: %s. step: %s.', s.start, s.stop, s.step );
// => 'start: 3. stop: null. step: -1.'
s = seq2slice( 'end/2:', 5, false );
console.log( 'start: %s. stop: %s. step: %s.', s.start, s.stop, s.step );
// => 'start: 2. stop: 5. step: 1.'
See Also
@stdlib/slice-base/seq2multislice
: convert a multidimensional subsequence string to a MultiSlice object.@stdlib/slice-base/slice2seq
: convert a Slice object to a subsequence string.
Notice
This package is part of stdlib, a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.
For more information on the project, filing bug reports and feature requests, and guidance on how to develop stdlib, see the main project repository.
Community
License
See LICENSE.
Copyright
Copyright © 2016-2024. The Stdlib Authors.