kuldarim kuldarim - 7 months ago 16
Javascript Question

Order array by predefined rules

I have an array of currencies

["GBP", "EUR", "NOK", "DKK", "SKE", "USD", "SEK", "BGN"]
. I would like to order it by moving predefined list if the currency is present to the beginning of array. Predefined list is
['EUR', 'USD', 'DKK', 'SKE', 'NOK', 'GBP']
So in this case it should return
['EUR', 'USD', 'DKK', 'SKE', 'NOK', 'GBP', 'SEK', BGN']

But in case unfiltered array does not contain all values in predifined list it should also order it correctly. For example :
["GBP", "EUR", "NOK", "LTU", "ZGN"]
should look like
['EUR', 'NOK', 'GBP', 'LTU', 'ZGN'

I was trying to sort it using this function:

list.sort(c => ['EUR', 'USD', 'DKK', 'SKE', 'NOK', 'GBP'].indexOf(c))

but it puts all predefined currencies at the end of the list, not at the from. Maybe there is a better way of doing that?


You could use sorting with map and a hash table for the sort order. If the value is not in the hash table, the original order is taken.

var order = ['EUR', 'USD', 'DKK', 'SKE', 'NOK', 'GBP'],
    orderObj = Object.create(null),
    data = ["GBP", "EUR", "NOK", "DKK", "SKE", "USD", "SEK", "BGN"];

// generate hash table
order.forEach((a, i) => orderObj[a] = i + 1);

// temporary array holds objects with position and sort-value
var mapped = data.map((el, i) => { return { index: i, value: orderObj[el] || Infinity }; });

// sorting the mapped array containing the reduced values
mapped.sort((a, b) => a.value - b.value || a.index - b.index);

// assigning the resulting order
var data = mapped.map(el => data[el.index]);