Fastest way to generate delimited string from 1d numpy array

Question

I have a program which needs to turn many large one-dimensional numpy arrays of floats into delimited strings. I am finding this operation quite slow relative to the mathema

Answer 1

numpy.savetxt is even slower than string.join. ndarray.tofile() doesn't seem to work with StringIO.

But I do find a faster method (at least applying to OP's example on python2.5 with lower version of numpy):

import numpy as np
x = np.random.randn(100000)
for i in range(100):
    (",%f"*100000)[1:] % tuple(x)

It looks like string format is faster than string join if you have a well defined format such as in this particular case. But I wonder why OP needs such a long string of floating numbers in memory.

Newer versions of numpy shows no speed improvement.