Generate a frequency table according to an indicator function.
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> Generate a frequency table according to an indicator function.
``bash`
npm install @stdlib/utils-async-tabulate-by
`javascript`
var tabulateByAsync = require( '@stdlib/utils-async-tabulate-by' );
#### tabulateByAsync( collection, \[options,] indicator, done )
Generates a frequency table according to an indicator function (i.e., a function which specifies how to categorize an element in the input collection).
`javascript
function indicator( value, next ) {
setTimeout( onTimeout, value );
function onTimeout() {
console.log( value );
next( null, (value > 2000) );
}
}
function done( error, result ) {
if ( error ) {
throw error;
}
console.log( result );
}
var arr = [ 3000, 2500, 1000, 750 ];
tabulateByAsync( arr, indicator, done );
/* =>
750
1000
2500
3000
[ [ false, 2, 0.5 ], [ true, 2, 0.5 ] ]
*/
`
The returned frequency table is an array of arrays. Each sub-array corresponds to a unique value in the input collection and is structured as follows:
- 0: unique value1
- : value count2
- : frequency percentage
The function accepts the following options:
- limit: the maximum number of pending invocations at any one time. Default: infinity.series
- : boolean indicating whether to sequentially invoke the indicator function for each collection element. If true, the function sets options.limit=1. Default: false.thisArg
- : the execution context for indicator.
By default, all elements are processed concurrently, which means that the function does not guarantee completion order. To process each collection element sequentially, set the series option to true.
`javascript
function indicator( value, next ) {
setTimeout( onTimeout, value );
function onTimeout() {
console.log( value );
next( null, (value > 2000) );
}
}
function done( error, result ) {
if ( error ) {
throw error;
}
console.log( result );
}
var arr = [ 3000, 2500, 1000, 750 ];
var opts = {
'series': true
};
tabulateByAsync( arr, opts, indicator, done );
/* =>
3000
2500
1000
750
[ [ true, 2, 0.5 ], [ false, 2, 0.5 ] ]
*/
`
To limit the maximum number of pending function invocations, set the limit option.
`javascript
function indicator( value, next ) {
setTimeout( onTimeout, value );
function onTimeout() {
console.log( value );
next( null, (value > 2000) );
}
}
function done( error, result ) {
if ( error ) {
throw error;
}
console.log( result );
}
var arr = [ 3000, 2500, 1000, 750 ];
var opts = {
'limit': 2
};
tabulateByAsync( arr, opts, indicator, done );
/* =>
2500
3000
1000
750
[ [ true, 2, 0.5 ], [ false, 2, 0.5 ] ]
*/
`
To set the execution context of the indicator function, set the thisArg option.
`javascript
function indicator( value, next ) {
this.count += 1;
setTimeout( onTimeout, value );
function onTimeout() {
next( null, (value > 2000) );
}
}
var arr = [ 3000, 2500, 1000, 750 ];
var context = {
'count': 0
};
var opts = {
'thisArg': context
};
tabulateByAsync( arr, opts, indicator, done );
function done( error, result ) {
if ( error ) {
throw error;
}
console.log( result );
// => [ [ false, 2, 0.5 ], [ true, 2, 0.5 ] ]
console.log( context.count );
// => 4
}
`
When invoked, the indicator function is provided a maximum of four arguments:
- value: collection value.
- index: collection index.
- collection: the input collection.indicator
- next: a callback which should be called once the function has finished processing a collection value.
The actual number of provided arguments depends on function length. If the indicator function accepts two arguments, the indicator function is provided value and next. If the indicator function accepts three arguments, the indicator function is provided value, index, and next. For every other indicator function signature, the indicator function is provided all four arguments.
`javascript
function indicator( value, i, collection, next ) {
console.log( 'collection: %s. %d: %d', collection.join( ',' ), i, value );
setTimeout( onTimeout, value );
function onTimeout() {
console.log( value );
next( null, (value > 2000) );
}
}
function done( error, result ) {
if ( error ) {
throw error;
}
console.log( result );
}
var arr = [ 3000, 2500, 1000, 750 ];
tabulateByAsync( arr, indicator, done );
/* =>
collection: 3000,2500,1000,750. 0: 3000
collection: 3000,2500,1000,750. 1: 2500
collection: 3000,2500,1000,750. 2: 1000
collection: 3000,2500,1000,750. 3: 750
750
1000
2500
3000
[ [ false, 2, 0.5 ], [ true, 2, 0.5 ] ]
*/
`
#### tabulateByAsync.factory( \[options,] indicator )
Returns a function which invokes an indicator function once for each element in a collection and generates a frequency table.
`javascript
function indicator( value, next ) {
setTimeout( onTimeout, value );
function onTimeout() {
console.log( value );
next( null, (value > 2000) );
}
}
function done( error, result ) {
if ( error ) {
throw error;
}
console.log( result );
}
var f = tabulateByAsync.factory( indicator );
var arr1 = [ 3000, 2500, 1000, 750 ];
f( arr1, done );
/* =>
750
1000
2500
3000
[ [ false, 2, 0.5 ], [ true, 2, 0.5 ] ]
*/
var arr2 = [ 300, 250, 100 ];
f( arr2, done );
/* =>
100
250
300
[ [ false, 3, 1.0 ] ]
*/
`
The function accepts the same options as tabulateByAsync().
- A collection may be either an [Array][mdn-array], [Typed Array][mdn-typed-array], or an array-like [Object][mdn-object] (excluding strings and functions).next
- If a provided function calls the callback with a truthy error argument, the function suspends execution and immediately calls the done callback for subsequent error handling.collection
- The function does not support dynamic resizing.undefined
- The function does not skip elements.collection
- If provided an empty , the function calls the done callback with an empty array for the tabulated results.tabulateByAsync
- Neither nor the function returned by the factory method guarantee asynchronous execution. To guarantee asynchrony, wrap the done callback in a function which either executes at the end of the current stack (e.g., nextTick) or during a subsequent turn of the event loop (e.g., setImmediate, setTimeout).
`javascript
var resolve = require( 'path' ).resolve;
var readFile = require( '@stdlib/fs-read-file' );
var tabulateByAsync = require( '@stdlib/utils-async-tabulate-by' );
var files = [
resolve( __dirname, 'package.json' ),
resolve( __dirname, 'README.md' ),
resolve( __dirname, 'beep.boop.md' )
];
function done( error, result ) {
if ( error ) {
throw error;
}
console.log( result );
}
function indicator( file, next ) {
var opts = {
'encoding': 'utf8'
};
readFile( file, opts, onFile );
function onFile( error ) {
if ( error ) {
return next( null, 'nonreadable' );
}
next( null, 'readable' );
}
}
tabulateByAsync( files, indicator, done );
`
*
- [@stdlib/utils-async/count-by][@stdlib/utils/async/count-by]: group values according to an indicator function and return group counts.
- [@stdlib/utils-async/group-by][@stdlib/utils/async/group-by]: group values according to an indicator function.
- [@stdlib/utils-tabulate-by][@stdlib/utils/tabulate-by]: generate a frequency table according to an indicator function.
*
This package is part of [stdlib][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][stdlib], see the main project [repository][stdlib].
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---
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