如何设置str(numpi .float64)的精度?

i need to write a couple of numpy floats to a csv-file which has additional string content. therefore i dont use savetxt etc. with numpy.set_printoptions() i can only define the print behaviour, but not the str() behaviour. i know that i miss something and it cant be that hard, but i dont find a reasonable answer on the interwebs. maybe someone can point me in the right direction. heres some example code:

我需要写几个浮点数到一个csv文件，它有附加的字符串内容。因此，我不能使用numpy.set_printoptions()来使用savetxt，我只能定义打印行为，但不能定义str()行为。我知道我错过了什么，也没那么难，但我在网上找不到一个合理的答案。也许有人能给我指明正确的方向。这是一些示例代码:

In [1]: import numpy as np
In [2]: foo = np.array([1.22334])

In [3]: foo
Out[3]: array([ 1.22334])

In [4]: foo[0]
Out[4]: 1.2233400000000001

In [5]: str(foo[0])
Out[5]: '1.22334'

In [6]: np.set_printoptions(precision=3)

In [7]: foo
Out[7]: array([ 1.223])

In [8]: foo[0]
Out[8]: 1.2233400000000001

In [9]: str(foo[0])
Out[9]: '1.22334'

How do i convert np.float to a nicely formatted string, which i can feed to file.write()?

如何转换np。浮动到一个格式良好的字符串，我可以将其提供给file.write()?

kind regards,

亲切的问候,

fookatchu

5 个解决方案

#1

You can just use standard string formatting:

您可以使用标准的字符串格式:

>>> x = 1.2345678
>>> '%.2f' % x
'1.23'

#2

You could use normal String formating, see: http://docs.python.org/library/string.html#formatspec

您可以使用普通的字符串格式，参见:http://docs.python.org/library/string.html#formatspec

Example:

例子:

print '{:.2f}'.format(0.1234)  # '0.12'
print '{:.2e}'.format(0.1234)  # '1.23e-01'

#3

Instead of str(foo[0]), use "%.3f" % foo[0].

使用“%”代替str(foo[0])。3 f % foo[0]。

#4

Numpy 1.14 and later have format_float_positional and format_float_scientific functions to format a floating-point scalar as a decimal string in positional or scientific notation, with control over rounding, trimming and padding. These functions offer much more control to the formatting than conventional Python string formatters.

Numpy 1.14和稍后有format_float_position和format_float_scientific函数，以位置或科学符号将浮点标量格式化为十进制字符串，并控制舍入、修剪和填充。与传统的Python字符串格式器相比，这些函数提供了更多的格式化控制。

import numpy as np

x = np.float64('1.2345678')
print(np.format_float_positional(x))  # 1.2345678
print(np.format_float_positional(x, precision=3))  # 1.235
print(np.format_float_positional(np.float16(x)))  # 1.234
print(np.format_float_positional(np.float16(x), unique=False, precision=8))  # 1.23437500

y = x / 1e8
print(np.format_float_scientific(y))  # 1.2345678e-08
print(np.format_float_scientific(y, precision=3, exp_digits=1))  # 1.235e-8

etc.

等。

These advanced formatters are based on the Dragon4 algorithm; see Ryan Juckett's Printing Floating-Point Numbers to read more on the subject.

这些高级格式器基于Dragon4算法;请参阅Ryan Juckett印刷的浮点数来了解更多关于这个主题的内容。

#5

Also you can do:

你也可以做的事:

precision = 2
str(np.round(foo[0], precision))

It had some advantages for me over the ('%.2f' % x) when I needed to do string a str(np.log(0.0)) which is neatly treated to "-inf" by numpy so you don't have to bother here.

它比%对我有一些好处。2f' % x)当我需要执行一个str(np.log(0.0))时，它被numpy巧妙地处理为“-inf”，这样你就不用麻烦了。

#1