Question

From a text file containing three columns of data I want to be able to just take a slice of data from all three columns where the values in the first column are equal to the values defined in above. I then want to put the slice of data into a new array called slice (I am using Python 2.7)

above = range(18000, 18060, 5)

data = np.loadtxt(open('data.txt'), delimiter=None)

energies = (np.hsplit(data, 3))[0]

slice = set(energies)&set(above)

The above comes back with:

Traceback (most recent call last):
  File "<pyshell#27>", line 1, in <module>
    set(energies)&set(above)
TypeError: unhashable type: 'numpy.ndarray

Answer 1

Your variable energies probably has the wrong shape:

>>> from numpy import array
>>> set([1,2,3]) & set(range(2, 10))
set([2, 3])
>>> set(array([1,2,3])) & set(range(2,10))
set([2, 3])
>>> set(array([[1,2,3],])) & set(range(2,10))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unhashable type: 'numpy.ndarray'

And that’s what happens if you read columnar data using your approach:

>>> data
array([[  1.,   2.,   3.],
       [  3.,   4.,   5.],
       [  5.,   6.,   7.],
       [  8.,   9.,  10.]])
>>> hsplit(data,3)[0]
array([[ 1.],
       [ 3.],
       [ 5.],
       [ 8.]])

Probably you can simply use

>>> data[:,0]
array([ 1.,  3.,  5.,  8.])

instead.

(P.S. Your code looks like it’s undecided about whether it’s data or elementdata. I’ve assumed it’s simply a typo.)