Range extraction: Difference between revisions

====Idiomatic====

<lang JavaScript>

function toRange(arr) {

const ranges = [];

const sorted = [...arr.filter(Number.isInteger)].sort((x,y) => Math.sign(x-y));

const sequenceBreak = (x,y) => y - x > 1 ;

let i = 0;

while ( i < sorted.length ) {

let j = i ;

while ( j < sorted.length - 1 && !sequenceBreak( sorted[j], sorted[j+1] ) ) {

++j;

}

const from = sorted[i];

const thru = sorted[j];

const rangeLen = 1 + j - i;

if ( from === thru ) {

ranges.push( [from] );

} else {

if ( rangeLen > 2 ) {

ranges.push([from,thru]);

} else {

ranges.push([from], [thru]);

}

}

i = j+1;

}

return ranges.map( range => range.join('-') ).join(',');

}

// -----------------------------------------------------------------------------

// Test Case

// -----------------------------------------------------------------------------

const expected = '0-2,4,6-8,11,12,14-25,27-33,35-39';

const actual = toRange([

0, 1, 2,

4,

6, 7, 8,

11, 12, // should be two singletons

14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25,

27, 28, 29, 30, 31, 32, 33,

35, 36, 37, 38, 39,

]);

console.log(`actual output : '${actual}'.`);

console.log(`expected output : '${expected}'.`);

console.log(`Correct? ${ actual === expected ? 'Yes' : 'No'}`);

</lang>

{{Out}}

<pre>

actual output : '0-2,4,6-8,11,12,14-25,27-33,35-39'.

expected output : '0-2,4,6-8,11,12,14-25,27-33,35-39'.

Correct? Yes

</pre>

====From Haskell====