val_a, val_b = 0, 0 t = None while i < len(a) or j < len(b): a_next = a[i][0] if i < len(a) else float('inf') b_next = b[j][0] if j < len(b) else float('inf') if a_next < b_next: val_a = a[i][1] t = a[i][0] i += 1 elif b_next < a_next: val_b = b[j][1] t = b[j][0] j += 1 else: val_a = a[i][1] val_b = b[j][1] t = a[i][0] i += 1 j += 1 result.append((t, val_a + val_b)) return result

This code merges two sorted lists of timestamps with corresponding values a and b into a single list, summing the values when the timestamps match.

Variables val_a and val_b store the last known values from lists a and b. The iteration goes through both lists simultaneously, comparing the current timestamps. If a timestamp from one list is smaller, the corresponding value and time are updated; if they are equal, both values and the time are updated.

The result is a list of tuples (t, val_a + val_b), where t is the time, and the sum is the total of the values from both lists at that moment.

Example:

# a and b are lists of tuples (time, value), sorted by time
# Result — merging with summing values by time