7.2.4. Indexing TimeSeries

This section shows how to use these methods for indexing TimeSeries:

• ktk.TimeSeries.get_index_at_time

• ktk.TimeSeries.get_index_before_time

• ktk.TimeSeries.get_index_after_time

• ktk.TimeSeries.get_index_at_event

• ktk.TimeSeries.get_index_before_event

• ktk.TimeSeries.get_index_after_event

For this section, we will continue to use kinetic data from wheelchair propulsion:

import kineticstoolkit.lab as ktk
import matplotlib.pyplot as plt

ts = ktk.load(ktk.doc.download("kinetics_wheelchair_propulsion_events.ktk.zip"))
ts.plot()

Despite the title of this section, we do not index or slice a TimeSeries. Instead, we address its time or data arrays, as for any NumPy array. For instance, to get the time and force data at the 100th sample of the TimeSeries, we would do:

print("Time is", ts.time[99])
print("Force is", ts.data["Forces"][99])

Time is 0.4125
Force is [ 0.27 -1.93  0.41  0.  ]

We may however want to know search which index corresponds to a given time. To this effect, we can use ktk.TimeSeries.get_index_at_time, ktk.TimeSeries.get_index_before_time and ktk.TimeSeries.get_index_after_time:

print("The index that is nearest to 15 seconds is:")
print(ts.get_index_at_time(15.0))

print("The index that is just before 15 seconds is:")
print(ts.get_index_before_time(15.0))

print("The index that is just after 15 seconds is:")
print(ts.get_index_after_time(15.0))

The index that is nearest to 15 seconds is:
3600
The index that is just before 15 seconds is:
3599
The index that is just after 15 seconds is:
3601

Or, we may want to know which index corresponds to a given event, using ktk.TimeSeries.get_index_at_event, ktk.TimeSeries.get_index_before_event or ktk.TimeSeries.get_index_after_event:

print("The index that is nearest to 2nd push is:")
print(ts.get_index_at_event("push", occurrence=1))

print("The index that is just before 2nd push is:")
print(ts.get_index_before_event("push", occurrence=1))

print("The index that is just after 2nd push is:")
print(ts.get_index_after_event("push", occurrence=1))

The index that is nearest to 2nd push is:
2520
The index that is just before 2nd push is:
2519
The index that is just after 2nd push is:
2521

The get_index_before_... and get_index_after_... methods have a parameter inclusive that selects if the selection is inclusive (<=, >=) or exclusive (<, >):

Method	Returns
get_index_before_time(t, inclusive=False)	index for nearest time \(<\) t
get_index_before_time(t, inclusive=True)	index for nearest time \(<=\) t
get_index_after_time(t, inclusive=False)	index for nearest time \(>\) t
get_index_after_time(t, inclusive=True)	index for nearest time \(>=\) t
get_index_before_event(name, occurrence, inclusive=False)	index for nearest time \(<\) event time
get_index_before_event(name, occurrence, inclusive=True)	index for nearest time \(<=\) event time
get_index_after_event(name, occurrence, inclusive=False)	index for nearest time \(>\) event time
get_index_after_event(name, occurrence, inclusive=True)	index for nearest time \(>=\) event time