numpy csv import problem

Question

I am having some difficulty with importing data from a .csv file. I am simply trying to import the data and print the max value. Here is my code:

>>> x, y = numpy.loadtxt('data.csv', delimiter=',', usecols=(4,5), unpack=True)
>>> print 'max =', max(x)

When I enter the above code, I get the following error message:

TypeError: 'numpy.float64' object is not iterable

I tried to change the data type using the dtype=int argument, but it threw the same error. Does anyone have any idea what could be the problem? Thanks in advance for your help!

If your file only contains a single line, loadtxt() unfortunately returns a scalar for x and y instead of an array with a single entry. Is there only one line in your file? — Sven Marnach
– Sven Marnach, Commented Jun 5, 2011 at 14:44
The data.csv file contains one row of data with numerous columns. Is the solution to add more rows to the 'data.csv` file? — drbunsen
– drbunsen, Commented Jun 5, 2011 at 14:56

Sven Marnach · Accepted Answer · 2011-06-05 15:02:56Z

4

The output of loadtxt() is unfortunately a bit inconistent: If there is only one line in your file, x and y will be scalars, but for more than one line, they will be arrays. The Python built-in max() only works for iterables, so it only works in the latter case.

Using the Python built-in max() function instead of numpy.max() is inefficient for NumPy arrays anyway. So a solution is to use

print x.max()

or

print numpy.max(x)

in the second line.

answered Jun 5, 2011 at 15:02

Sven Marnach

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1 Comment

drbunsen Over a year ago

Thank you! This was very helpful. I appreciate you taking the time to explain things so clearly.

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