Suppress Scientific Notation in Numpy When Creating Array From Nested List

Question

I have a nested Python list that looks like the following:

my_list = [[3.74, 5162, 13683628846.64, 12783387559.86, 1.81],
 [9.55, 116, 189688622.37, 26033226         


        

Answer 1

Python Force-suppress all exponential notation when printing numpy ndarrays, wrangle text justification, rounding and print options:

What follows is an explanation for what is going on, scroll to bottom for code demos.

Passing parameter suppress=True to function set_printoptions works only for numbers that fit in the default 8 character space allotted to it, like this:

import numpy as np
np.set_printoptions(suppress=True) #prevent numpy exponential 
                                   #notation on print, default False

#            tiny     med  large
a = np.array([1.01e-5, 22, 1.2345678e7])  #notice how index 2 is 8 
                                          #digits wide

print(a)    #prints [ 0.0000101   22.     12345678. ]

However if you pass in a number greater than 8 characters wide, exponential notation is imposed again, like this:

np.set_printoptions(suppress=True)

a = np.array([1.01e-5, 22, 1.2345678e10])    #notice how index 2 is 10
                                             #digits wide, too wide!

#exponential notation where we've told it not to!
print(a)    #prints [1.01000000e-005   2.20000000e+001   1.23456780e+10]

numpy has a choice between chopping your number in half thus misrepresenting it, or forcing exponential notation, it chooses the latter.

Here comes set_printoptions(formatter=...) to the rescue to specify options for printing and rounding. Tell set_printoptions to just print bare a bare float:

np.set_printoptions(suppress=True,
   formatter={'float_kind':'{:f}'.format})

a = np.array([1.01e-5, 22, 1.2345678e30])  #notice how index 2 is 30
                                           #digits wide.  

#Ok good, no exponential notation in the large numbers:
print(a)  #prints [0.000010 22.000000 1234567799999999979944197226496.000000] 

We've force-suppressed the exponential notation, but it is not rounded or justified, so specify extra formatting options:

np.set_printoptions(suppress=True,
   formatter={'float_kind':'{:0.2f}'.format})  #float, 2 units 
                                               #precision right, 0 on left

a = np.array([1.01e-5, 22, 1.2345678e30])   #notice how index 2 is 30
                                            #digits wide

print(a)  #prints [0.00 22.00 1234567799999999979944197226496.00]

The drawback for force-suppressing all exponential notion in ndarrays is that if your ndarray gets a huge float value near infinity in it, and you print it, you're going to get blasted in the face with a page full of numbers.

Full example Demo 1:

from pprint import pprint
import numpy as np
#chaotic python list of lists with very different numeric magnitudes
my_list = [[3.74, 5162, 13683628846.64, 12783387559.86, 1.81],
           [9.55, 116, 189688622.37, 260332262.0, 1.97],
           [2.2, 768, 6004865.13, 5759960.98, 1.21],
           [3.74, 4062, 3263822121.39, 3066869087.9, 1.93],
           [1.91, 474, 44555062.72, 44555062.72, 0.41],
           [5.8, 5006, 8254968918.1, 7446788272.74, 3.25],
           [4.5, 7887, 30078971595.46, 27814989471.31, 2.18],
           [7.03, 116, 66252511.46, 81109291.0, 1.56],
           [6.52, 116, 47674230.76, 57686991.0, 1.43],
           [1.85, 623, 3002631.96, 2899484.08, 0.64],
           [13.76, 1227, 1737874137.5, 1446511574.32, 4.32],
           [13.76, 1227, 1737874137.5, 1446511574.32, 4.32]]

#convert python list of lists to numpy ndarray called my_array
my_array = np.array(my_list)

#This is a little recursive helper function converts all nested 
#ndarrays to python list of lists so that pretty printer knows what to do.
def arrayToList(arr):
    if type(arr) == type(np.array):
        #If the passed type is an ndarray then convert it to a list and
        #recursively convert all nested types
        return arrayToList(arr.tolist())
    else:
        #if item isn't an ndarray leave it as is.
        return arr

#suppress exponential notation, define an appropriate float formatter
#specify stdout line width and let pretty print do the work
np.set_printoptions(suppress=True,
   formatter={'float_kind':'{:16.3f}'.format}, linewidth=130)
pprint(arrayToList(my_array))

Prints:

array([[           3.740,         5162.000,  13683628846.640,  12783387559.860,            1.810],
       [           9.550,          116.000,    189688622.370,    260332262.000,            1.970],
       [           2.200,          768.000,      6004865.130,      5759960.980,            1.210],
       [           3.740,         4062.000,   3263822121.390,   3066869087.900,            1.930],
       [           1.910,          474.000,     44555062.720,     44555062.720,            0.410],
       [           5.800,         5006.000,   8254968918.100,   7446788272.740,            3.250],
       [           4.500,         7887.000,  30078971595.460,  27814989471.310,            2.180],
       [           7.030,          116.000,     66252511.460,     81109291.000,            1.560],
       [           6.520,          116.000,     47674230.760,     57686991.000,            1.430],
       [           1.850,          623.000,      3002631.960,      2899484.080,            0.640],
       [          13.760,         1227.000,   1737874137.500,   1446511574.320,            4.320],
       [          13.760,         1227.000,   1737874137.500,   1446511574.320,            4.320]])

Full example Demo 2:

import numpy as np  
#chaotic python list of lists with very different numeric magnitudes 

#            very tiny      medium size            large sized
#            numbers        numbers                numbers

my_list = [[0.000000000074, 5162, 13683628846.64, 1.01e10, 1.81], 
           [1.000000000055,  116, 189688622.37, 260332262.0, 1.97], 
           [0.010000000022,  768, 6004865.13,   -99e13, 1.21], 
           [1.000000000074, 4062, 3263822121.39, 3066869087.9, 1.93], 
           [2.91,            474, 44555062.72, 44555062.72, 0.41], 
           [5,              5006, 8254968918.1, 7446788272.74, 3.25], 
           [0.01,           7887, 30078971595.46, 27814989471.31, 2.18], 
           [7.03,            116, 66252511.46, 81109291.0, 1.56], 
           [6.52,            116, 47674230.76, 57686991.0, 1.43], 
           [1.85,            623, 3002631.96, 2899484.08, 0.64], 
           [13.76,          1227, 1737874137.5, 1446511574.32, 4.32], 
           [13.76,          1337, 1737874137.5, 1446511574.32, 4.32]] 
import sys 
#convert python list of lists to numpy ndarray called my_array 
my_array = np.array(my_list) 
#following two lines do the same thing, showing that np.savetxt can 
#correctly handle python lists of lists and numpy 2D ndarrays. 
np.savetxt(sys.stdout, my_list, '%19.2f') 
np.savetxt(sys.stdout, my_array, '%19.2f') 

Prints:

 0.00             5162.00      13683628846.64      10100000000.00              1.81
 1.00              116.00        189688622.37        260332262.00              1.97
 0.01              768.00          6004865.13 -990000000000000.00              1.21
 1.00             4062.00       3263822121.39       3066869087.90              1.93
 2.91              474.00         44555062.72         44555062.72              0.41
 5.00             5006.00       8254968918.10       7446788272.74              3.25
 0.01             7887.00      30078971595.46      27814989471.31              2.18
 7.03              116.00         66252511.46         81109291.00              1.56
 6.52              116.00         47674230.76         57686991.00              1.43
 1.85              623.00          3002631.96          2899484.08              0.64
13.76             1227.00       1737874137.50       1446511574.32              4.32
13.76             1337.00       1737874137.50       1446511574.32              4.32
 0.00             5162.00      13683628846.64      10100000000.00              1.81
 1.00              116.00        189688622.37        260332262.00              1.97
 0.01              768.00          6004865.13 -990000000000000.00              1.21
 1.00             4062.00       3263822121.39       3066869087.90              1.93
 2.91              474.00         44555062.72         44555062.72              0.41
 5.00             5006.00       8254968918.10       7446788272.74              3.25
 0.01             7887.00      30078971595.46      27814989471.31              2.18
 7.03              116.00         66252511.46         81109291.00              1.56
 6.52              116.00         47674230.76         57686991.00              1.43
 1.85              623.00          3002631.96          2899484.08              0.64
13.76             1227.00       1737874137.50       1446511574.32              4.32
13.76             1337.00       1737874137.50       1446511574.32              4.32

Notice that rounding is consistent at 2 units precision, and exponential notation is suppressed in both the very large e+x and very small e-x ranges.

Answer 2

I guess what you need is np.set_printoptions(suppress=True), for details see here: http://pythonquirks.blogspot.fr/2009/10/controlling-printing-in-numpy.html

For SciPy.org numpy documentation, which includes all function parameters (suppress isn't detailed in the above link), see here: https://docs.scipy.org/doc/numpy/reference/generated/numpy.set_printoptions.html

Answer 3

for 1D and 2D arrays you can use np.savetxt to print using a specific format string:

>>> import sys
>>> x = numpy.arange(20).reshape((4,5))
>>> numpy.savetxt(sys.stdout, x, '%5.2f')
 0.00  1.00  2.00  3.00  4.00
 5.00  6.00  7.00  8.00  9.00
10.00 11.00 12.00 13.00 14.00
15.00 16.00 17.00 18.00 19.00

Your options with numpy.set_printoptions or numpy.array2string in v1.3 are pretty clunky and limited (for example no way to suppress scientific notation for large numbers). It looks like this will change with future versions, with numpy.set_printoptions(formatter=..) and numpy.array2string(style=..).

Answer 4

You could write a function that converts a scientific notation to regular, something like

def sc2std(x):
    s = str(x)
    if 'e' in s:
        num,ex = s.split('e')
        if '-' in num:
            negprefix = '-'
        else:
            negprefix = ''
        num = num.replace('-','')
        if '.' in num:
            dotlocation = num.index('.')
        else:
            dotlocation = len(num)
        newdotlocation = dotlocation + int(ex)
        num = num.replace('.','')
        if (newdotlocation < 1):
            return negprefix+'0.'+'0'*(-newdotlocation)+num
        if (newdotlocation > len(num)):
            return negprefix+ num + '0'*(newdotlocation - len(num))+'.0'
        return negprefix + num[:newdotlocation] + '.' + num[newdotlocation:]
    else:
        return s