[Numpy-discussion] loadtxt and usecols

Irvin Probst irvin.probst at ensta-bretagne.fr
Tue Nov 10 11:39:05 EST 2015

On 10/11/2015 16:52, Daπid wrote:
> ((((42,))))  is exactly the same as (42,) If you want a tuple of 
> tuples, you have to do ((42,),), but then it raises: TypeError: list 
> indices must be integers, not tuple.

My bad, I wrote that too fast, please forget this.

> I think loadtxt should be a tool to read text files in the least 
> surprising fashion, and a text file is a 1 or 2D container, so it 
> shouldn't return any other shapes.

And I *do* agree with the "shouldn't return any other shapes" part of 
your phrase. What I was trying to say, admitedly with a very bogus 
example, is that either loadtxt() should always output an array whose 
shape matches the shape of the object passed to usecol or it should 
never do it, and I'm if favor of never.
I'm perfectly aware that what I suggest would break the current behavior 
of usecols=(2,) so I know it does not have the slightest probability of 
being accepted but still, I think that the "least surprising fashion" is 
to always return an 2-D array because for many, many, many people a text 
data file has N lines and M columns and N=1 or M=1 is not a specific case.

Anyway I will of course modify my PR according to any decision made here.

In your example:
> a=[[[2,],[],[],],[],[],[]]
> foo=np.loadtxt("CONCARNEAU_2010.txt", usecols=a)
> What would the shape of foo be?

As I said in my previous email:

 > should just work and return me a 2-D (or 1-D if you like) array with 
the data I asked for

So, 1-D or 2-D it is up to you, but as long as there is no ambiguity in 
which columns the user is asking for it should imho work.


More information about the NumPy-Discussion mailing list