Writing both float and integer on a text file from one numpy array

Question

I have a nxm numpy array that either has positive values with 8 decimal points like 0.02113342 or NoValue data that is -9999. I am using the line below to make a text file from the numpy array

numpy.savetxt("result.asc", Numpy_Array, fmt="%.8f")#2D array to ASCII

However, I will have -9999.00000000 instead of -9999. I open the file and replace those numbers with -9999 using the following code:

with file("result.asc", 'r') as original: 
    data = original.read()
    new = data.replace(str(-9999)+".00000000", str(-9999))
with file("result.asc", 'w') as modified:
    modified.write(new)

Is there a more elegant way to write -9999 rather than -9999.00000000 from the beginning instead of opening the whole file again and replacing them?

The ASCII file will be much bigger and there is no value to it! :) — ahoosh
– ahoosh, Commented Aug 4, 2014 at 15:17

Community · Accepted Answer · 2017-05-23 12:11:39Z

5

Try fmt="%.8g". It is not the same as "%.8f" for all floating point values (e.g. for very small values, it uses exponential notation), but it might work for the cases you have. (See the table at https://docs.python.org/2/library/string.html#format-specification-mini-language with the floating point types--scroll down a bit--for an explanation of the difference between the f and g formats.)

In [188]: x
Out[188]: 
array([[    0.20134635, -9999.        ],
       [    0.9287082 ,     0.00000123],
       [    0.77482316,     0.27246281],
       [    0.40529746,     0.41133371]])

In [189]: np.savetxt("xf.dat", x, fmt="%.8f")

In [190]: np.savetxt("xg.dat", x, fmt="%.8g")

In [191]: !cat xf.dat
0.20134635 -9999.00000000
0.92870820 0.00000123
0.77482316 0.27246281
0.40529746 0.41133371

In [192]: !cat xg.dat
0.20134635 -9999
0.9287082 1.2345679e-06
0.77482316 0.27246281
0.40529746 0.41133371

Here's the actual value of x[1,1]:

In [193]: x[1,1]
Out[193]: 1.23456789e-06

Alternatively, take a look at this answer to a similar question: How to format in numpy savetxt such that zeros are saved only as "0"

edited May 23, 2017 at 12:11

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answered Aug 4, 2014 at 15:43

Warren Weckesser

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2 Comments

ahoosh Over a year ago

It totally worked! Perfect! Can you please add an explanation about the differences between fmt="%.8g" and fmt="%.8f" in your answer?

Warren Weckesser Over a year ago

@bikhaab: I added a link to the Python documentation.

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