formatPrefix will sometimes not perform rounding

[jdharrisnz]

For example: d3.formatPrefix(',.2', 1e3)(1555) produces 1.55, should be 1.56.

This is likely a simple fix, but unfortunately I'm not adept enough to figure out the source code and submit a PR, sorry.

[jdharrisnz]

This appears to be a problem with Chrome's .toFixed() function, where numbers ending in 5 won't round up. The workaround is to use Math.round() before calling .toFixed().

This seems to require an update to the f type in formatTypes.js.

So for the above case it would be:
(Math.round(1.555*100)/100).toFixed(2)

And in the generalised sense:
"f": (x, p) => (Math.round(x * Number('1e' + i)) / Number('1e' + i)).toFixed(p)

[Fil]

I'm seeing the same behavior with Firefox and Safari. See https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/toFixed, which has a detailed explanation (for 2.55).

[mbostock]

Working as intended.

[mbostock]

Well, (1.555).toFixed(2) producing "1.55" is the intended behavior. But I guess d3.formatPrefix introducing rounding error is not intended.

[jdharrisnz]

I made a local branch to submit a PR but I don't have write access.

The needed change is to formatTypes.js.

"f": (x, p) => (Math.round(x * Number('1e' + p)) / Number('1e' + p)).toFixed(p);

My earlier comment had i instead of p for some reason, oops.