collapse cell in jupyter notebook

You can create a cell and put the following code in it:

%%html
<style>
div.input {
    display:none;
}
</style>

Running this cell will hide all input cells. To show them back, you can use the menu to clear all outputs.

Otherwise you can try notebook extensions like below:

https://github.com/ipython-contrib/IPython-notebook-extensions/wiki/Home_3x

I had a similar issue and the "nbextensions" pointed out by @Energya worked very well and effortlessly. The install instructions are straight forward (I tried with anaconda on Windows) for the notebook extensions and for their configurator.

That said, I would like to add that the following extensions should be of interest.

• Hide Input | This extension allows hiding of an individual codecell in a notebook. This can be achieved by clicking on the toolbar button:

• Collapsible Headings | Allows notebook to have collapsible sections, separated by headings

• Codefolding | This has been mentioned but I add it for completeness

UPDATE:

The newer jupyter-lab is a more modern and feature-rich interface which supports cell folding by default. See @intsco's answer below

UPDATE 2

Since jupyter-lab now also supports extensions, you can extend the built-in cell-folding functionality with the Collapsible_Headings extension.

Original answer:

The jupyter contrib nbextensions Python package contains a code-folding extension that can be enabled within the notebook. Follow the link (Github) for documentation.

To install using command line:

pip install jupyter_contrib_nbextensions
jupyter contrib nbextension install --user

To make life easier in managing them, I'd also recommend the jupyter nbextensions configurator package. This provides an extra tab in your Notebook interface from where you can easily (de)activate all installed extensions.

Installation:

pip install jupyter_nbextensions_configurator
jupyter nbextensions_configurator enable --user

JupyterLab supports cell collapsing. Clicking on the blue cell bar on the left will fold the cell.