Configure relative to a base_dir

1. Import dependencies

We need to import the classes and functions that we will be using from the corresponding packages.

[ ]:
import os
from os.path import join, isfile, isdir
from urllib.request import urlretrieve
from anndata import read_h5ad

from vitessce import (
    Component as cm,
    CoordinationType as ct,
from vitessce.data_utils import (

2. Define a base_dir

We will define a base_dir inside which our data will live. We will provide this to VitessceConfig in order to construct a configuration that contains URL paths relative to this directory.

[ ]:
BASE_DIR = "data"

3. Download the data

For this example, we need to download a dataset from the COVID-19 Cell Atlas

[ ]:
adata_relative_filepath = "habib17.processed.h5ad" # Relative to BASE_DIR
adata_filepath = join(BASE_DIR, adata_relative_filepath)
if not isfile(adata_filepath):
    os.makedirs(BASE_DIR, exist_ok=True)
    urlretrieve('', adata_filepath)

4. Load the data

Note: this function may print a FutureWarning

[ ]:
adata = read_h5ad(adata_filepath)

4.1. Preprocess the Data For Visualization

This dataset contains 25,587 genes. We prepare to visualize the top 50 highly variable genes for the heatmap as ranked by dispersion norm, although one may use any boolean array filter for the heatmap.

[ ]:
top_dispersion = adata.var["dispersions_norm"][
        key=lambda k: adata.var["dispersions_norm"][k],
adata.var["top_highly_variable"] = (
    adata.var["dispersions_norm"] > top_dispersion

4.2 Save the Data to Zarr store

We want to convert the original h5ad file to a Zarr store, which Vitessce is able to load. We can use the optimize_adata function to ensure that all arrays and dataframe columns that we intend to use in our visualization are in the optimal format to be loaded by Vitessce. This function will cast arrays to numerical data types that take up less space (as long as the values allow). Note: unused arrays and columns (i.e., not specified in any of the parameters to optimize_adata) will not be copied into the new AnnData object.

[ ]:
zarr_relative_filepath = "habib17.processed.zarr" # Relative to BASE_DIR
zarr_filepath = join(BASE_DIR, zarr_relative_filepath)
if not isdir(zarr_filepath):
    adata = optimize_adata(
    adata.write_zarr(zarr_filepath, chunks=[adata.shape[0], VAR_CHUNK_SIZE])

5. Create the Vitessce widget configuration

Vitessce needs to know which pieces of data we are interested in visualizing, the visualization types we would like to use, and how we want to coordinate (or link) the views.

5.1. Instantiate a VitessceConfig object

Use the VitessceConfig constructor to create an instance. In this case, we want to construct our configuration using local data that is relative to a particular directory, so we provide the base_dir parameter.

Note: This base_dir parameter is optional. When it is omitted, local data paths are assumed to be relative to the current working directory.

[ ]:
vc = VitessceConfig(schema_version="1.0.15", name='Habib et al', base_dir=BASE_DIR)

5.2. Add a dataset to the VitessceConfig instance

In Vitessce, a dataset is a container for one file per data type. The .add_dataset(name) method on the vc instance sets up and returns a new dataset instance.

Then, we can call the dataset’s .add_object(wrapper_object) method to attach a “data wrapper” instance to our new dataset. For example, the AnnDataWrapper helps to configure AnnData Zarr stores for use in the Vitessce configuration.

Dataset wrapper classes may require additional parameters to resolve ambiguities. For instance, AnnData objects may store multiple clusterings or cell type annotation columns in the adata.obs dataframe. We can use the parameter obs_set_paths to tell Vitessce that certain columns of the obs dataframe correspond to cell type annotations or cell clusterings.

[ ]:
dataset = vc.add_dataset(name='Brain').add_object(AnnDataWrapper(
        adata_path=zarr_relative_filepath, # Relative to BASE_DIR (because we specified base_dir in the VitessceConfig constructor)
        obs_set_names=["Cell Type"],

5.3. Add visualizations to the VitessceConfig instance

Now that we have added a dataset, we can configure visualizations. The .add_view method adds a view (i.e. visualization or controller component) to the configuration.

The Component enum class (which we have imported as cm here) can be used to fill in the component_type parameter.

For convenience, the SCATTERPLOT component type takes the extra mapping keyword argument, which specifies which embedding should be used for mapping cells to (x,y) points on the plot.

[ ]:
scatterplot = vc.add_view(cm.SCATTERPLOT, dataset=dataset, mapping="UMAP")
cell_sets = vc.add_view(cm.OBS_SETS, dataset=dataset)
genes = vc.add_view(cm.FEATURE_LIST, dataset=dataset)
heatmap = vc.add_view(cm.HEATMAP, dataset=dataset)

5.4. Define the visualization layout

The vc.layout(view_concat) method allows us to specify how our views will be arranged in the layout grid in the widget. The | and / characters are magic syntax for hconcat(v1, v2) and vconcat(v1, v2), respectively.

[ ]:
vc.layout((scatterplot | cell_sets) / (heatmap | genes));

6. Create the widget

The vc.widget() method returns the configured widget instance.

[ ]:
vw = vc.widget()

7. Check the URLs in the configuration

We can check that the data URLs in the configuration respected the specified base_dir.

[ ]:
config_dict = vc.to_dict(base_url=BASE_URL_PLACEHOLDER)