'''This module provides function for working with significant
figures.
written by Chris Burn, http://users.obs.carnegiescience.edu/~cburns/site/?p=22
'''
import types,re,string
epat = re.compile(r'^([^e]+)e(.+)$')
def round_sig(x, n):
'''round floating point x to n significant figures'''
if type(n) is not int:
raise TypeError("n must be an integer")
try:
x = float(x)
except:
raise TypeError("x must be a floating point object")
form = "%0." + str(n-1) + "e"
st = form % x
num,expo = epat.findall(st)[0]
expo = int(expo)
fs = string.split(num,'.')
if len(fs) < 2:
fs = [fs[0],""]
if expo == 0:
return num
elif expo > 0:
if len(fs[1]) < expo:
fs[1] += "0"*(expo-len(fs[1]))
st = fs[0]+fs[1][0:expo]
if len(fs[1][expo:]) > 0:
st += '.'+fs[1][expo:]
return st
else:
expo = -expo
if fs[0][0] == '-':
fs[0] = fs[0][1:]
sign = "-"
else:
sign = ""
return sign+"0."+"0"*(expo-1)+fs[0]+fs[1]
def round_sig_error(x, ex, n, paren=False):
'''Find ex rounded to n sig-figs and make the floating point x
match the number of decimals. If [paren], the string is
returned as quantity(error) format'''
stex = round_sig(ex,n)
if stex.find('.') < 0:
extra_zeros = len(stex) - n
sigfigs = len(str(int(x))) - extra_zeros
stx = round_sig(x,sigfigs)
else:
num_after_dec = len(string.split(stex,'.')[1])
stx = ("%%.%df" % num_after_dec) % (x)
if paren:
if stex.find('.') >= 0:
stex = stex[stex.find('.')+1:]
return "%s(%s)" % (stx,stex)
return stx,stex
def format_table(cols, errors, n, labels=None, headers=None, latex=False):
'''Format a table such that the errors have n significant
figures. [cols] and [errors] should be a list of 1D arrays
that correspond to data and errors in columns. [n] is the number of
significant figures to keep in the errors. [labels] is an optional
column of strings that will be in the first column. [headers] is
an optional list of column headers. If [latex] is true, format
the table so that it can be included in a LaTeX table '''
if len(cols) != len(errors):
raise ValueError("Error: cols and errors must have same length")
ncols = len(cols)
nrows = len(cols[0])
if headers is not None:
if labels is not None:
if len(headers) == ncols:
headers = [""] + headers
elif len(headers) == ncols+1:
pass
else:
raise ValueError("length of headers should be %d" % (ncols+1))
else:
if len(headers) != ncols:
raise ValueError("length of headers should be %d" % (ncols))
if labels is not None:
if len(labels) != nrows:
raise ValueError("length of labels should be %d" % (nrows))
strcols = []
for col,error in zip(cols,errors):
strcols.append([])
strcols.append([])
for i in range(nrows):
val,err = round_sig_error(col[i], error[i], n)
strcols[-2].append(val)
strcols[-1].append(err)
lengths = [max([len(item) for item in strcol]) for strcol in strcols]
format = ""
if labels is not None:
format += "%%%ds " % (max(map(len, labels)))
if latex:
format += "& "
for length in lengths:
format += "%%%ds " % (length)
if latex:
format += "& "
if latex:
format = format[:-2] + " \\\\"
output = []
if headers:
if labels:
hs = [headers[0]]
for head in headers[1:]:
hs.append(head)
hs.append('+/-')
else:
hs = []
for head in headers:
hs.append(head)
hs.append('+/-')
output.append(format % tuple(hs))
for i in range(nrows):
if labels is not None:
output.append(format % tuple([labels[i]] + [strcol[i] for strcol in strcols]))
else:
output.append(format % tuple([strcol[i] for strcol in strcols]))
return output
def round_sig_error2(x, ex1, ex2, n):
'''Find min(ex1,ex2) rounded to n sig-figs and make the floating point x
and max(ex,ex2) match the number of decimals.'''
minerr = min(ex1,ex2)
minstex = round_sig(minerr,n)
if minstex.find('.') < 0:
extra_zeros = len(minstex) - n
sigfigs = len(str(int(x))) - extra_zeros
stx = round_sig(x,sigfigs)
maxstex = round_sig(max(ex1,ex2),sigfigs)
else:
num_after_dec = len(string.split(minstex,'.')[1])
stx = ("%%.%df" % num_after_dec) % (x)
maxstex = ("%%.%df" % num_after_dec) % (max(ex1,ex2))
if ex1 < ex2:
return stx,minstex,maxstex
else:
return stx,maxstex,minstex
