Usage

var invertBy = require( '@stdlib/utils-object-inverse-by' );

invertBy( obj, [options,] transform )

Inverts an object, such that keys become values and values become keys, according to a transform function.

function transform( key, value ) {
    return value;
}
var obj = {
    'a': 'beep',
    'b': 'boop'
};
var out = invertBy( obj, transform );
// returns { 'beep': 'a', 'boop': 'b' }

The function accepts the following options:

• duplicates: boolean indicating whether to store keys mapped to duplicate values in arrays. Default: true.

By default, keys mapped to duplicate values are stored in arrays.

function transform( key, value ) {
    return value;
}
var obj = {
    'a': 'beep',
    'b': 'beep'
};
var out = invertBy( obj, transform );
// returns { 'beep': [ 'a', 'b' ] }

To not allow duplicates, set the duplicates option to false. The output key-value pair will be the key most recently inserted into the input object.

function transform( key, value ) {
    return value;
}
var obj = {};
obj.a = 'beep';
obj.b = 'boop';
obj.c = 'beep'; // inserted after `a`

var opts = {
    'duplicates': false
};
var out = invertBy( obj, opts, transform );
// returns { 'beep': 'c', 'boop': 'b' }

The transform function is provided three arguments:

• key: object key
• value: object value corresponding to key
• obj: input object

function transform( key, value, o ) {
    if ( key === 'name' ) {
        return value;
    }
    return o.name + ':' + value;
}
var obj = {
    'name': 'foo',
    'a': 'beep',
    'b': 'boop'
};
var out = invertBy( obj, transform );
// returns { 'foo': 'name', 'foo:beep': 'a', 'foo:boop': 'b' }