Hi,
2009/11/18 Jason Heeris <jason.hee...@gmail.com>:
> In gnuplot, I can do the following:
>
> set format x "%.0s %cHz"
>
> ...and this will set the x-axis labels (on a semilogx style plot) to
> be "10 Hz", "100 Hz", "1 kHz", "10 kHz", etc.
I ended up implementing this myself, it wasn't too hard. I've attached
the code if anyone else is interested. I don't know matplotlib that
well, so I don't know if there's much duplication of code in there.
I thought I'd CC the dev list in case others think it might be useful.
If not, sorry for the noise.
Cheers,
Jason
import math, decimal
from matplotlib.ticker import LogFormatter
# The SI engineering prefixes
ENG_PREFIXES = {
-24: "y",
-21: "z",
-18: "a",
-15: "f",
-12: "p",
-9: "n",
-6: u"\u03BC", # Greek letter mu
-3: "m",
0: "",
3: "k",
6: "M",
9: "G",
12: "T",
15: "P",
18: "E",
21: "Z",
24: "Y"
}
def format_eng(num, places=0):
""" Formats a number in engineering notation, appending a letter
representing the power of 1000 of the original number. Some examples:
>>> format_eng(0, 0)
'0'
>>> format_eng(1000000, 1)
'1.0 M'
>>> format_eng("-1e-6", 2)
u'-1.00 \u03bc'
@param num: the value to represent
@type num: either a numeric value or a string that can be converted to a
numeric value (as per decimal.Decimal constructor)
@param prec: the number of decimal places to include (default 0)
@type prec: integer > 0
@return: engineering formatted string
"""
dnum = decimal.Decimal(str(num))
sign = 1
if dnum < 0:
sign = -1
dnum = -dnum
if dnum != 0:
pow10 = decimal.Decimal(int(math.floor(dnum.log10()/3)*3))
else:
pow10 = decimal.Decimal(0)
pow10 = pow10.min(max(ENG_PREFIXES.keys()))
pow10 = pow10.max(min(ENG_PREFIXES.keys()))
prefix = ENG_PREFIXES[int(pow10)]
mant = sign*dnum/(10**pow10)
format_str = "%f %s"
if places > 0:
format_str = ("%%.%if %%s" % places)
else:
format_str = "%i %s"
formatted = format_str % (mant, prefix)
return formatted.strip()
class EngFormatter(LogFormatter):
"""
Formats axis values using engineering prefixes to represent powers of 1000,
plus a specified unit, eg. 10 MHz instead of 1e7.
"""
def __init__(self, unit=""):
LogFormatter.__init__(self, base=10)
self.unit = unit
def __call__(self, x, pos=None):
# only label the decades
b=self._base
fx = math.log(abs(x))/math.log(b)
isDecade = self.is_decade(fx)
if not isDecade and self.labelOnlyBase:
s = ''
else:
s = "%s%s" % (format_eng(x, 0), self.units)
return self.fix_minus(s)
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