Rounding to significant figures in numpy

Question

I\'ve tried searching this and can\'t find a satisfactory answer.

I want to take a list/array of numbers and round them all to n significant figures. I have written

Answer 1

Okay, so reasonably safe to say this is not allowed for in standard functionality. To close this off then, this is my attempt at a robust solution. It's rather ugly/non-pythonic and prob illustrates better then anything why I asked this question, so please feel free to correct or beat :)

import numpy as np

def round2SignifFigs(vals,n):
    """
    (list, int) -> numpy array
    (numpy array, int) -> numpy array

    In: a list/array of values
    Out: array of values rounded to n significant figures

    Does not accept: inf, nan, complex

    >>> m = [0.0, -1.2366e22, 1.2544444e-15, 0.001222]
    >>> round2SignifFigs(m,2)
    array([  0.00e+00,  -1.24e+22,   1.25e-15,   1.22e-03])
    """

    if np.all(np.isfinite(vals)) and np.all(np.isreal((vals))):
        eset = np.seterr(all='ignore')
        mags = 10.0**np.floor(np.log10(np.abs(vals)))  # omag's
        vals = np.around(vals/mags,n)*mags             # round(val/omag)*omag
        np.seterr(**eset)
        vals[np.where(np.isnan(vals))] = 0.0           # 0.0 -> nan -> 0.0
    else:
        raise IOError('Input must be real and finite')
    return vals

Nearest I get to neat does not account for 0.0, nan, inf or complex:

>>> omag      = lambda x: 10**np.floor(np.log10(np.abs(x)))
>>> signifFig = lambda x, n: (np.around(x/omag(x),n)*omag(x))

giving:

>>> m = [0.0, -1.2366e22, 1.2544444e-15, 0.001222]
>>> signifFig(m,2)
array([ nan, -1.24e+22,   1.25e-15,   1.22e-03])