| Andrew Cooke | Contents | Latest | RSS | Twitter | Previous | Next

C[omp]ute

Welcome to my blog, which was once a mailing list of the same name and is still generated by mail. Please reply via the "comment" links.

Always interested in offers/projects/new ideas. Eclectic experience in fields like: numerical computing; Python web; Java enterprise; functional languages; GPGPU; SQL databases; etc. Based in Santiago, Chile; telecommute worldwide. CV; email.

Personal Projects

Lepl parser for Python.

Colorless Green.

Photography around Santiago.

SVG experiment.

Professional Portfolio

Calibration of seismometers.

Data access via web services.

Cache rewrite.

Extending OpenSSH.

C-ORM: docs, API.

Last 100 entries

Payroll Service Quotes for Cat Soft LLC; (Beating Dead Horse) StackOverflow; Current State of Justice in China; Now Is Cat Soft LLC's Chance To Save Up To 32% On Mail; Axiom of Determinacy; Ewww; Fee Chaos Book; Course on Differential Geometry; Increase Efficiency with GPS Vehicle Tracking for Cat Soft LLC; Okay, but...; Sparse Matrices, Deep Learning; Sounds Bad; Applebaum Rape; Tomato Chutney v4; Have to add...; Culturally Liberal and Nothing More; Weird Finite / Infinite Result; Your diamond is a beaten up mess; Maths Books; Good Bike Route from Providencia / Las Condes to Panul\; Iain Pears (Author of Complex Plots); Plum Jam; Excellent; More Recently; For a moment I forgot StackOverflow sucked; A Few Weeks On...; Chilean Book Recommendations; How To Write Shared Libraries; Jenny Erpenbeck (Author); Dijkstra, Coins, Tables; Python libraries error on OpenSuse; Deserving Trump; And Smugness; McCloskey Economics Trilogy; cmocka - Mocks for C; Concept Creep (Americans); Futhark - OpenCL Language; Moved / Gone; Fan and USB issues; Burgers in Santiago; The Origin of Icosahedral Symmetry in Viruses; autoenum on PyPI; Jars Explains; Tomato Chutney v3; REST; US Elections and Gender: 24 Point Swing; PPPoE on OpenSuse Leap 42.1; SuperMicro X10SDV-TLN4F/F with Opensuse Leap 42.1; Big Data AI Could Be Very Bad Indeed....; Cornering; Postcapitalism (Paul Mason); Black Science Fiction; Git is not a CDN; Mining of Massive Data Sets; Rachel Kaadzi Ghansah; How great republics meet their end; Raspberry, Strawberry and Banana Jam; Interesting Dead Areas of Math; Later Taste; For Sale; Death By Bean; It's Good!; Tomato Chutney v2; Time ATAC MX 2 Pedals - First Impressions; Online Chilean Crafts; Intellectual Variety; Taste + Texture; Time Invariance and Gauge Symmetry; Jodorowsky; Tomato Chutney; Analysis of Support for Trump; Indian SF; TP-Link TL-WR841N DNS TCP Bug; TP-Link TL-WR841N as Wireless Bridge; Sending Email On Time; Maybe run a command; Sterile Neutrinos; Strawberry and Banana Jam; The Best Of All Possible Worlds; Kenzaburo Oe: The Changeling; Peach Jam; Taste Test; Strawberry and Raspberry Jam; flac to mp3 on OpenSuse 42.1; Also, Sebald; Kenzaburo Oe Interview; Otake (Kitani Minoru) move Black 121; Is free speech in British universities under threat?; I am actually good at computers; Was This Mansplaining?; WebFaction / LetsEncrypt / General Disappointment; Sensible Philosophy of Science; George Ellis; Misplaced Intuition and Online Communities; More Reading About Japan; Visibilty / Public Comments / Domestic Violence; Ferias de Santiago; More (Clearly Deliberate); Deleted Obit Post; And then a 50 yo male posts this...; We Have Both Kinds Of Contributors

© 2006-2015 Andrew Cooke (site) / post authors (content).

Auto-Scaling Date Axes in Python

From: andrew cooke <andrew@...>

Date: Wed, 28 Jul 2010 10:16:53 -0400

There's a nice algorithm for auto-scaling axes, called the "nice number
algorithm", written by Paul Heckbert and published in "Graphics Gems" -
http://books.google.com/books?id=fvA7zLEFWZgC&pg=PA61&lpg=PA61&dq=nice+numbers+graphics+gems&source=bl&ots=7LdCq3nI-j&sig=L8qoZ8l_a95KAtHmMjagJ8cC0U0&hl=en&ei=KDhQTKLwGcT48AbTsvnEAQ&sa=X&oi=book_result&ct=result&resnum=2&ved=0CBYQ6AEwAQ#v=onepage&q&f=false

The routines below implement this, but are parameterised over the number base
used, so can also be used for axes based on units that repeat over multiples
of 12, 60, or any other value.


from calendar import timegm
from math import floor, log, log10, ceil
from time import gmtime

# These allow the use with base 10, 12 and 60:
LIM10 = (10, [(1.5, 1), (3, 2), (7, 5)], [1, 2, 5])
LIM12 = (12, [(1.5, 1), (3, 2), (8, 6)], [1, 2, 6])
LIM60 = (60, [(1.5, 1), (20, 15), (40, 30)], [1, 15, 40])

def heckbert_d(lo, hi, ntick=5, limits=None):
    '''
    Calculate the step size.
    '''
    if limits is None:
        limits = LIM10
    (base, rfs, fs) = limits
    def nicenum(x, round):
        step = base ** floor(log(x)/log(base))
        f = float(x) / step
        nf = base
        if round:
            for (a, b) in rfs:
                if f < a:
                    nf = b
                    break
        else:
            for a in fs:
                if f <= a:
                    nf = a
                    break
        return nf * step
    delta = nicenum(hi-lo, False)
    return nicenum(delta / (ntick-1), True)

def heckbert(lo, hi, ntick=5, limits=None):
    '''
    Calculate the axes lables.
    '''
    def _heckbert():
        d = heckbert_d(lo, hi, ntick=ntick, limits=limits)
        graphlo = floor(lo / d) * d
        graphhi = ceil(hi / d) * d
        fmt = '%' + '.%df' %  max(-floor(log10(d)), 0)
        value = graphlo
        while value < graphhi + 0.5*d:
            yield fmt % value
            value += d
    return list(_heckbert())


This can then be used with a range of seconds as follows:


def autoscale_time(start, end):
    '''
    Yields a sequence of epochs that are nicely spaced.

    start and end are Unix epochs.
    '''
    time_chunks = [('days', 3 * 24 * 60 * 60, 24 * 60 * 60, 2, None),
                   ('hours', 3 * 60 * 60, 60 * 60, 3, LIM12),
                   ('minutes', 3 * 60, 60, 4, LIM60),
                   ('seconds', 0, 1, 5, LIM60)]
    for (name, limit, secs, sindex, limits) in self.time_chunks:
	if (end - start) > limit:
	    break
    d = heckbert_d(start / secs, end / secs, limits=limits)

    # zero out lower steps, so that we get a starting date that's an
    # integral number of units
    stime = list(gmtime(start))
    for i in range(sindex, 9):
	stime[i] = 0

    # generate a sequence of epochs (cannot use the usual heckbert routine 
    # because formatting will be different)
    value = timegm(stime)
    while value <= end:
	if value >= start:
            yield value
	value += d * secs


This could be extended further by:

- having different formats in the time_chunks parameter, so that different
  intervals are formatted differently

- adding months etc.  This would require changing the "secs" increment to be a
  timedelta and working with datetime instances rather than epochs (because
  months are not all equally sized).


NOTE: The code above is cut + pasted from some working code and is not tested
in its existing form; I may have introduced a bug somewhere, but hopefully
this illustrates the idea.

Andrew

Comment on this post