cellxgene/docs/getting-started.md

getting started

You'll need python 3.6+ and Google Chrome. The web UI is tested on OSX and Windows using Chrome, and the python CLI is tested on OSX and Ubuntu (via WSL/Windows). It should work on other platforms, but if you run into trouble let us know.

To install run

pip install cellxgene

To start exploring a dataset call

cellxgene launch dataset.h5ad --open

If you want an example dataset download this file and then call

cellxgene launch pbmc3k.h5ad --open

On Mac OS and Ubuntu, you should see your web browser open with the following

Note: automatic opening of the browser with the --open flag only works on OS X, on other platforms you'll need to directly point to the provided link in your browser.

There are several options available, such as:

• --layout to specify the layout as tsne, umap, diffmap, phate, draw_graph_fa, or draw_graph_fr
• --title to show a title on the explorer
• --open to automatically open the web browser after launching (OS X only)

To see all options call

cellxgene launch --help

There is an additional subcommand called cellxgene prepare that takes an existing dataset in one of several formats and applies minimal preprocessing and reformatting so that launch can use it (see the next section for more info on prepare).

data formatting

requirements

The launch command assumes that the data is stored in the .h5ad format from the anndata library. It also assumes that certain computations have already been performed. Briefly, the .h5ad format wraps a two-dimensional ndarray and stores additional metadata as "annotations" for either observations (referred to as obs and obsm) or variables (var and varm). cellxgene launch makes the following assumptions about your data (we recommend loading and inspecting your data using scanpy to validate these assumptions)

• an obs field has a unique identifier for every cell (you can specify which field to use with the --obs-names option, by default it will use the value of data.obs_names)
• a var field has a unique identifier for every gene (you can specify which field to use with the --var-names option, by default it will use the value of data.var_names)
• an obsm field contains the two-dimensional coordinates for the layout that you want to render (e.g. X_umap for the umap layout)
• any additional obs fields will be rendered as per-cell continuous or categorical metadata by the app (e.g. louvain cluster assignments)

prepare

The prepare command is included to help you format your data. It uses scanpy under the hood. This is especially useful if you are starting with raw unanalyzed data and are unfamiliar with scanpy.

To prepare from an existing .h5ad file use

cellxgene prepare dataset.h5ad --output=dataset-processed.h5ad

This will load the input data, perform PCA and nearest neighbor calculations, compute umap and tsne layouts and louvain cluster assignments, and save the results in a new file called dataset-processed.h5ad that can be loaded using cellxgene launch. Data can be loaded from several formats, including .h5ad .loom and a 10-Genomics-formatted mtx directory. Several options are available, including running one of the preprocessing recipes included with scanpy, which include steps like cell filtering and gene selection. To learn more about the recipes please see the scanpy documentation.

Depending on the options chosen, prepare can take a long time to run (a few minutes for datasets with 10-100k cells, up to an hour or more for datasets with >100k cells). If you want prepare to run faster we recommend using the sparse option and only computing the layout for umap, using a call like this

cellxgene prepare dataset.h5ad --output=dataset-processed.h5ad --layout=umap --sparse

To see all options call

cellxgene prepare --help

Note: cellxgene prepare will only perform louvain clustering if you have the python-igraph and louvain packages installed. To make sure they are installed alongside cellxgene use

pip install cellxgene[louvain]

If the aforementioned optional package installation fails, you can also install these packages directly:

pip install python-igraph louvain>=0.6

conda and virtual environments

If you use conda and want to create a conda environment for cellxgene you can use the following commands

conda create --yes -n cellxgene python=3.7
conda activate cellxgene
pip install cellxgene

Or you can create a virtual environment by using

ENV_NAME=cellxgene
python3.7 -m venv ${ENV_NAME}
source ${ENV_NAME}/bin/activate
pip install cellxgene

docker

We have included a dockerfile to conveniently run cellxgene from docker.

1. Build the image docker build . -t cellxgene
2. Run the container and mount data docker run -v "$PWD/example-dataset/:/data/" -p 5005:5005 cellxgene launch --host 0.0.0.0 data/pbmc3k.h5ad
   • You will need to use --host 0.0.0.0 to have the container listen to incoming requests from the browser