Round to closest list value?

EvanReese

Does anyone know of a way that I can take a number and round it to the nearest value in a predetermined list (maybe an array)? For example:

if my list is [1,4,8,11,12]
1.9 rounds to 1
9.3 rounds to 8
9.5 rounds to 11
11.6 rounds to 12

There's got to be a name for such a thing.

john_mcclary

There are a few rounding funcitons

ceil() rounds up to  nearest whole number
floor() rounds down to nearest whole number
round() rounds to nearest up or down to nearest whole number
roundToPrecision() will round with decimals

var listStart = [1.9859,9.23,9.2525,11.652,0.654110111];     
        var listFloor = [];
        var listCeil = [];
        var listRound = [];
        var listRoundToPrecision = [];
        
        for (var item in listStart)
        {
            listFloor = append(listFloor, floor(item));
            listCeil = append(listCeil, ceil(item));
            listRound = append(listRound, round(item));
            listRoundToPrecision = append(listRoundToPrecision, roundToPrecision(item, 2));
        }
        
        println("Original List: " ~ listStart);
        println("Rounded List Down: " ~ listFloor);
        println("Rounded List Up: " ~ listCeil);
        println("Rounded List Nearest: " ~ listRound);
        println("Rounded List Nearest (2 place decimal): " ~ listRoundToPrecision);


// result \\
Original List: [ 1.9859 , 9.23 , 9.2525 , 11.652 , 0.654110111 ]
Rounded List Down: [ 1 , 9 , 9 , 11 , 0 ]
Rounded List Up: [ 2 , 10 , 10 , 12 , 1 ]
Rounded List Nearest: [ 2 , 9 , 9 , 12 , 1 ]
Rounded List Nearest (2 place decimal): [ 1.99 , 9.23 , 9.25 , 11.65 , 0.65 ]

konstantin_shiriazdanov

I have a function maxItem() which returns a max value of the list based on some other estimation function:

<pre class="CodeBlock"><code>function maxItem(container is array, estimationFunction is function)<br>{<br>&nbsp;&nbsp;&nbsp; var max = container[0];<br>&nbsp;&nbsp;&nbsp; for (var item in container)<br>&nbsp;&nbsp;&nbsp; {<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; if (estimationFunction(item) > estimationFunction(max))<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; {<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; max = item;<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; }<br>&nbsp;&nbsp;&nbsp; }<br>&nbsp;&nbsp;&nbsp; return max;<br>}

say we have a value "value" and estimation function may be:

const estFunction = function(x){return -abs(x - value)};

then you just do this:

const roundedItem = maxItem(roundedArr, estFunction);

ilya_baran

If your array is small, Konstantin's method works fine.  If you have a large array, the efficient method for solving this problem is binary search: https://en.wikipedia.org/wiki/Binary_search_algorithm#Procedure_for_finding_the_leftmost_element (use that procedure and then pick the closer one of A[L] and A[L-1])

EvanReese

Thanks for all the info everyone!