fill in 3D array

Robert Kern robert.kern at
Thu Jul 24 03:18:32 CEST 2008

knielsen73 at wrote:
> Hi,
> I am a python newbie, trying to convert my IDL scripts to python. I am
> kind of stuck at the moment. I am reading in a 1-D data file with 2000
> data points. I need to put them in a 3-D array with size [10,10,20]. I
> have defined the field array as arr = zeros((10,10,20)) but don't know
> how to read the data into the array.

I assume that you are using numpy. Use numpy.fromfile() and the .reshape() 
method. Assuming that your file is ASCII with numbers separated by whitespace:

   import numpy
   arr = numpy.fromfile(thefilename, sep=' ').reshape((10,10,20))

There is no need, in this case, to create an array before reading the data.

> Also, I need to extract a slice of a 3-D array and tried a =
> array_name(:,:,20) but that didn't work.

Python uses [] brackets for indexing, not ().


Robert Kern

"I have come to believe that the whole world is an enigma, a harmless enigma
  that is made terrible by our own mad attempt to interpret it as though it had
  an underlying truth."
   -- Umberto Eco

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