round to nearest nice number

Question

I\'m writing an application which requires rounding labels to the nearest \'nice\' number. I\'ll put some code below to demonstrate this, but my issue is that I was using a ser

Answer 1

I prefer the following over Groo's approach, as it rounds 267 to 275 instead of 500. It basically rounds to the first digit, and then the nearest quarter fraction of that power of 10.

static double round_pretty(double val) {
    var fraction = 1;
    var log = Math.floor(Math.log10(val));

    // This keeps from adding digits after the decimal
    if(log > 1) {
        fraction = 4;
    }

    return Math.round(val * fraction * Math.pow(10, -log)) 
        / fraction / Math.pow(10, -log);
}

The output is as follows:

0.01 -> 0.01
0.025 -> 0.03    (Groo's does 0.025)
0.1 -> 0.1
0.2 -> 0.2       (Groo's does 0.25)
0.49 -> 0.5
0.5 -> 0.5       (Groo's does 1)
0.51 -> 0.5      (Groo's does 1)
0.7 -> 0.7       (Groo's does 1)
1 -> 1
2 -> 2           (Groo's does 2.5)
9 -> 9
23.07 -> 20
25 -> 30
49 -> 50
50 -> 50         (Groo's does 100 here)
58 -> 60
94 -> 90
95 -> 100
99 -> 100
100 -> 100
109 -> 100       (Groo's does 250 here)
158 -> 150
249 -> 250
267 -> 275
832 -> 825
1234567 -> 1250000
1499999 -> 1500000
1625000 -> 1750000