CODEWITHSUNDEEP
pythonpython-xarray
jmilloy
jmilloy

Reputation: 8365

add dimension to an xarray DataArray

I need to add a dimension to a DataArray, filling the values across the new dimension. Here's the original array.

a_size = 10
a_coords = np.linspace(0, 1, a_size)

b_size = 5
b_coords = np.linspace(0, 1, b_size)

# original 1-dimensional array
x = xr.DataArray(
    np.random.random(a_size),
    coords=[('a', a coords)])

I guess I could create an empty DataArray with the new dimension and copy the existing data in.

y = xr.DataArray(
    np.empty((b_size, a_size),
    coords=([('b', b_coords), ('a', a_coords)])
y[:] = x

A better idea might be to be to use concat. It took me a while to figure out how to specify both the dims and the coords for the concat dimension, and none of these options seem great. Is there something I'm missing that can makes this version cleaner?

# specify the dimension name, then set the coordinates
y = xr.concat([x for _ in b_coords], 'b')
y['b'] = b_coords

# specify the coordinates, then rename the dimension
y = xr.concat([x for _ in b_coords], b_coords)
y.rename({'concat_dim': 'b'})

# use a DataArray as the concat dimension
y = xr.concat(
    [x for _ in b_coords],
    xr.DataArray(b_coords, name='b', dims=['b']))

Still, is there a better way to do this than either of the two above options?

Upvotes: 15

Views: 21638

Answers (4)

Q-man
Q-man

Reputation: 2209

If DA is your data array with length DimLen, you can now use expand_dims:

DA.expand_dims({'NewDim':DimLen})

Upvotes: 14

J.Warren
J.Warren

Reputation: 778

Using .assign_coords method will do it. However you can't assign coordinates to a non-existant dimension, the way to do as a one liner is:

y = x.expand_dims({b_coords.name: b_size}).assign_coords({b_coords.name: b_coords})

Upvotes: 4

chuaxr
chuaxr

Reputation: 308

With reference to the syntax of the question:

y = x.expand_dims({"b": b_coords})

Upvotes: 1

hackz
hackz

Reputation: 41

Because of the way that math is applied over new dimensions I like to multiply in order to add new dimensions.

identityb = xr.DataArray(np.ones_like(b_coords), coords=[('b', b_coords)])
y = x * identityb

Upvotes: 4

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