Add a description string to a numpy array

Question

I'd like to add a description to a python numpy array.

For example, when using numpy as an interactive data language, I'd like to do something like:

A = np.array([[1,2,3],[4,5,6]])
A.description = "Holds all the data from experiment 1. Each row contains an intensity measurement with the following columns: time [s], intensity [W/m^2], error [%]."

But it gives:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'numpy.ndarray' object has no attribute 'description'

Is this possible without subclassing the numpy.ndarray class?

Regards, Jonas

Maybe the simplest thing would be to make a class which contains the array and your description. That way you wouldn't have to subclass ndarray, which as you probably know is a bit wacky. — John Zwinck
– John Zwinck, Commented Oct 5, 2013 at 12:18
That would also be a more sensible way of making functions that deal with that data in the array. — rlms
– rlms, Commented Oct 5, 2013 at 12:21
If you don't want the description to survive array operations, subclassing work easily for this. If you want more, it requires a bit more and will leave a few operations where the information will not be preserved anyway. — seberg
– seberg, Commented Oct 6, 2013 at 9:04

Benjamin Loison · Accepted Answer · 2024-06-19 11:49:53Z

3

Simplest way would be to use a namedtuple to hold both the array and the description:

>>> from collections import namedtuple
>>> Array = namedtuple('Array', ['data', 'description'])
>>> A = Array(np.array([[1,2,3],[4,5,6]]), "Holds all the data from experiment 1. Each row contains an intensity measurement with the following columns: time [s], intensity [W/m^2], error [%].")
>>> A.data
array([[1, 2, 3],
       [4, 5, 6]])
>>> A.description
'Holds all the data from experiment 1. Each row contains an intensity measurement with the following columns: time [s], intensity [W/m^2], error [%].'

edited Jun 19, 2024 at 11:49

Benjamin Loison

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answered Oct 5, 2013 at 12:27

Ashwini Chaudhary

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1 Comment

Jonas Over a year ago

Nice. But probably I will write my own data class (like John Z. suggested), with a function to save and load the data and the description to a .dat file. Until this is done, the namedtuple will be my solution.

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