Add a way to merge duplicate cells

[ycanerol]

Sometimes we oversplit the cells during spike sorting, we need a way of merging them later.

• We need to define a standardized way of indicating duplicates/oversplit cells in the spike sheet.
• This should be reversible, so maybe we can merge contents of multiple spike time files into one and keep the originals as backup?

[dimokaramanlis]

This is how we do it usually (second bullet). We add a new line (in the Excel sheet) of the new cluster in the group of channels, giving it the next highest number (e.g. group of electrodes A has clusters 1,2,3,4 and the merger of 1+2 ends up as a new cluster 5). Then, we create a new raster file for cluster 5 of group A (for all stimuli), where we write sorted spikes for both clusters (1+2).