Custom Channel Sorting Orders

Use a custom sorting order when the columns of emgfile["RAW_SIGNAL"] do not follow the physical arrangement of the already available sorting orders.

A sorting order is a list of lists:

• the outer list represents grid columns, from left to right;
• each inner list represents positions within one column, from top to bottom;
• channel numbers refer to the columns of RAW_SIGNAL and must be base-0;
• np.nan represents a physical position without a channel.

For example, this grid has three rows and two columns:

	Column 0	Column 1
Row 0	0	3
Row 1	1	4
Row 2	2	5

Its sorting order is:

custom_sorting_order = [
    [0, 1, 2],  # Column 0
    [3, 4, 5],  # Column 1
]

Apply the Sorting Order

import openhdemg.library as emg

sorted_rawemg = emg.sort_rawemg(
    emgfile=emgfile,
    code="Custom order",
    custom_sorting_order=custom_sorting_order,
    dividebycolumn=True,
)

With dividebycolumn=True, the result is a dictionary containing col0, col1, and so on. With dividebycolumn=False, the result is one DataFrame, ordered column by column.

The orientation, n_rows, and n_cols arguments are not needed for a custom order because the grid shape is taken directly from custom_sorting_order.

Example: Alternating Channel Direction

Channel numbering sometimes changes direction between adjacent columns. The following synthetic grid uses an upward direction in its middle column:

	Column 0	Column 1	Column 2
Row 0	0	5	6
Row 1	1	4	7
Row 2	2	3	8

custom_sorting_order = [
    [0, 1, 2],
    [5, 4, 3],
    [6, 7, 8],
]

Example: Empty Grid Position

Use np.nan when the physical grid contains a position without a recorded channel:

	Column 0	Column 1
Row 0	0	4
Row 1	1	5
Row 2	2	6
Row 3	3	Empty

import numpy as np

custom_sorting_order = [
    [0, 1, 2, 3],
    [4, 5, 6, np.nan],
]

The sorted result contains an all-NaN column at the empty position. The original signal is not modified.

Quick Checks

Before sorting, make sure that:

• RAW_SIGNAL uses base-0 integer column names (0, 1, 2, ...);
• every recorded channel appears exactly once in the sorting order;
• all inner lists have the same length;
• empty physical positions use np.nan, not a channel number.

If a channel diagram uses base-1 numbering (1, 2, 3, ...), subtract one from each channel number before creating the sorting order.