issues: 257400162

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id node_id number title user state locked assignee milestone comments created_at updated_at closed_at author_association active_lock_reason draft pull_request body reactions performed_via_github_app state_reason repo type
257400162 MDU6SXNzdWUyNTc0MDAxNjI= 1572 Modifying data set resulting in much larger file size 1797906 closed 0     7 2017-09-13T14:24:06Z 2017-09-18T08:59:24Z 2017-09-13T17:12:28Z NONE      

I'm loading a 130MB nc file and applying a where mask to it to remove a significant amount of the floating points - replacing them with nan. However, when I go to save this file it has increased to over 500MB. If I load the original data set and instantly save it the file stays roughly the same size.

Here's how I'm applying the mask:

```python import os import xarray as xr

fp = 'ERA20c/swh_2010_01_05_05.nc' ds = xr.open_dataset(fp)

ds = ds.where(ds.latitude > 50)

head, ext = os.path.splitext(fp) xr.open_dataset(fp).to_netcdf('{}-duplicate{}'.format(head, ext)) ds.to_netcdf('{}-masked{}'.format(head, ext)) ```

Is there a way to reduce this file size of the masked dataset? I'd expect it to be roughly the same size or smaller.

Thanks.

 
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