string-differ

Description

A 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.

Installation

npm i string-differ

Usage

This library uses a rough implementation of Myers algorithm to calculate the shortest edit script between two strings. It assumes that a string can be converted to 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.

Note: string-differ v1 uses Levenshtein distance to compare strings and is usually slower than v2, especially for strings with smaller differences.

Generate Steps for Conversion

Character Operations

This method generates an operation for every 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 }
]

For delete and retain operations, the value field in the output contains the character's index in the base string (s1). However, for insert operations, the value field contains 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 }
]

For "Range" output type, the delete and retain operations will have startIndex and endIndex fields 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 for more information.