string-differ v1.0.0

string-differ

Description

A Javascript library to compare and transform strings. This library can:

• Generate operations to convert one string to another string.
• Apply a given set of operations to a string to transform it into another string.

This can be useful with operational-transforms implementaions.

Installation

npm i --save string-differ

Usage

This library uses a rough implementation of Levenshtein's algorithm to calculate the edit distance between two strings. It assumes that a string can be converted into another using 3 types of operations:

• insertion
• retention
• deletion

These types describe the operations that can be performed on string s1 to convert it to string s2.

Generate Steps for Conversion

Character Operations

Every step in the set of generated operations applies to one character in the base string (s1).

import { getStepsForTransformation } from 'string-differ';

const s1 = 'initial string';
const s2 = 'final string';

const steps = getStepsForTransformation("Char", { s1, s2 });

console.log(steps);

will output:

[
  { type: 'delete', value: 0 },
  { type: 'delete', value: 1 },
  { type: 'insert', value: 'f' },
  { type: 'retain', value: 2 },
  { type: 'delete', value: 3 },
  { type: 'delete', value: 4 },
  { type: 'insert', value: 'n' },
  { type: 'retain', value: 5 },
  { type: 'retain', value: 6 },
  { type: 'retain', value: 7 },
  { type: 'retain', value: 8 },
  { type: 'retain', value: 9 },
  { type: 'retain', value: 10 },
  { type: 'retain', value: 11 },
  { type: 'retain', value: 12 },
  { type: 'retain', value: 13 }
]

Please note that the value field in the above output represents the character's index in the base string (s1) for delete and retain operations, while for insert operations it specifies the character to be inserted.

Range Operations

This is a minor optimization over character operations. If the output type is specified as "Range", certain consecutive operations of the same type are grouped together.

import { getStepsForTransformation } from 'string-differ';

const s1 = 'initial string';
const s2 = 'final string';

const steps = getStepsForTransformation("Range", { s1, s2 });

console.log(steps);

will output:

[
  { type: 'delete', startIndex: 0, endIndex: 1 },
  { type: 'insert', value: 'f' },
  { type: 'retain', startIndex: 2, endIndex: 2 },
  { type: 'delete', startIndex: 3, endIndex: 4 },
  { type: 'insert', value: 'n' },
  { type: 'retain', startIndex: 5, endIndex: 13 }
]

Please note that for "Range" output type, the delete and retain operations will have a startIndex and endIndex field which represent the range of indices in the base string (s1). The insert operations, however, contain the value field which may specify one or more than one characters to be inserted.

Apply Operations to a String

Given a set of operations, and a base string (s1), the transformString function can be used to apply the steps to s1 to get the resultant string s2.

Range Operations

import { transformString } from 'string-differ';

const operations = [
  { type: 'delete', startIndex: 0, endIndex: 1 },
  { type: 'insert', value: 'f' },
  { type: 'retain', startIndex: 2, endIndex: 2 },
  { type: 'delete', startIndex: 3, endIndex: 4 },
  { type: 'insert', value: 'n' },
  { type: 'retain', startIndex: 5, endIndex: 13 }
];

const s1 = 'base string';

const s2 = transformString("Range", s1, operations);
console.log(s2);

will output:

'final string'

Character Operations

import { transformString } from 'string-differ';

const operations = [
  { type: 'delete', value: 0 },
  { type: 'delete', value: 1 },
  { type: 'insert', value: 'f' },
  { type: 'retain', value: 2 },
  { type: 'delete', value: 3 },
  { type: 'delete', value: 4 },
  { type: 'insert', value: 'n' },
  { type: 'retain', value: 5 },
  { type: 'retain', value: 6 },
  { type: 'retain', value: 7 },
  { type: 'retain', value: 8 },
  { type: 'retain', value: 9 },
  { type: 'retain', value: 10 },
  { type: 'retain', value: 11 },
  { type: 'retain', value: 12 },
  { type: 'retain', value: 13 }
];

const s1 = 'base string';

const s2 = transformString("Char", s1, operations);
console.log(s2);

will output:

'final string'

License

This library is distributed under the MIT License. See LICENSE.md for more information.