How to split and merge cells in JupyterLab

• JupyterLab: splitCell
  • Source
• In order to split one cell into many cells:
  • Place cursors where the split is desired, and then press and release ctrl + shift + -
  • Multiple cursors may be placed, by holding ctrl, and clicking the location for the cursor.

• JupyterLab: mergeCells
  • Source
• In order to merge multiple cells, into one cell:
  • Select the desired, consecutive cells, by holding shift, and clicking in the margin, where the [ ] is, which will highlight the selected cells.
  • While still holding shift, press m, and then release both keys.

• The resulting merged cell, will have a space between the code from each cell, as does the first image in this answer.
  • This is the expected behavior newModel.value.text = toMerge.join('\n\n');

For those that come here for Jupyter in VSCode, you can merge cells by:

1. Selecting the cells (using shift + arrow is supported)
2. Right click > Join With Previous Cell (or Join With Next Cell)

Join With Previous Cell key: Shift+Alt+Windows+J Join With Next Cell key: Alt+Windows+J

Note that it will join the selected range + previous or next cell. So, if you just want to merge two cell, no need to select using shift + arrow.