In SerialEM, one records image shift groups by including the navigator position in the output file name. Take for example the file
da_20190507_ProtX_2-2_126_0006_noDW.mrc. Here, I used the base name “da_20190507_ProtX_2-2” (for reasons), and SerialEM has added the navigator position (126) and the image number at this position (6). MotionCor2 also added “noDW.”
We usually employ a 9-hole image shift strategy, so the shift groups are indicated by the image number being 0001 - 0009. Splitting these files into shift groups can be supported trivially by specifying a field delimiter (e.g. “_”) and field index (e.g. 5) to select the group number.
The currently available splitting strategy should work, for example setting the index position to back, the start slice to 9, and considering 1 character, but it doesn’t work in practice. The output doesn’t show how the string is being parsed (for example you could bold the characters that will be used in the output display, to help the user get it right).