Fix interactive data selection when u2 is missing

Problem Description For interactive data selection, required topics are hard coded as u1, u2, u3, u4, and therefore makes the whole data selection fail if the topics are missing.

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Initialized dataframe with the following columns: 
['timestamp', 'u0', 'u1', 'u3', 'u4', 'u6', 'vx', 'vy', 'vz', 'q0', 'q1', 'q2', 'q3', 'ang_vel_x', 'ang_vel_y', 'ang_vel_z', 'ang_acc_b_x', 'ang_acc_b_y', 'ang_acc_b_z', 'acc_b_x', 'acc_b_y', 'acc_b_z', 'aux1', 'throttle', 'aileron', 'elevator', 'rudder', 'landed']
Data contains  37240 timestamps.
Computing force features for rotor
Computing moment features for rotor
Feature Computation |############################### | 37239/37240
Starting computation of aero moment features...
Feature Computation |############################### | 37239/37240
Cramer-Rao Bounds for force parameters:
puller_ct        0.07680642694482716
cl0      0.0012209864133548663
clalpha          0.012535964817765585
cldelta          0.006355243273722874
cd0      0.0010122110113291545
cdalpha          0.015118351468713459
cdalphasq        0.10865791831861082
Cramer-Rao Bounds for moment parameters:
puller_cmt       0.03374473061061396
cm0      0.002834858821845869
cmalpha          0.028497883320081425
cmdelta          0.01747374099395526
cmq      1.2087047286233417
['timestamp', 'u0', 'u1', 'u3', 'u4', 'u6']
inotify_add_watch(/home/jaeyoung/.config/ibus/bus/f7f12eb0d0ee44a092b8313f7b037850-unix-1) failed: (No space left on device)
Traceback (most recent call last):
  File "/home/jaeyoung/.local/lib/python3.6/site-packages/pandas/core/indexes/base.py", line 2898, in get_loc
    return self._engine.get_loc(casted_key)
  File "pandas/_libs/index.pyx", line 70, in pandas._libs.index.IndexEngine.get_loc
  File "pandas/_libs/index.pyx", line 101, in pandas._libs.index.IndexEngine.get_loc
  File "pandas/_libs/hashtable_class_helper.pxi", line 1675, in pandas._libs.hashtable.PyObjectHashTable.get_item
  File "pandas/_libs/hashtable_class_helper.pxi", line 1683, in pandas._libs.hashtable.PyObjectHashTable.get_item
KeyError: 'u2'

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "Tools/parametric_model/generate_parametric_model.py", line 152, in <module>
    start_model_estimation(**vars(arg_list))
  File "Tools/parametric_model/generate_parametric_model.py", line 102, in start_model_estimation
    model.load_dataframes(select_visual_data(model.data_df,visual_dataframe_selector_config_dict))
  File "/home/jaeyoung/dev/data-driven-dynamics/Tools/parametric_model/visual_dataframe_selector/data_selector.py", line 19, in select_visual_data
    w = MainWindow(data_df, plot_config_dict)
  File "/home/jaeyoung/dev/data-driven-dynamics/Tools/parametric_model/visual_dataframe_selector/src/main_window.py", line 47, in __init__
    self.setup_plots()
  File "/home/jaeyoung/dev/data-driven-dynamics/Tools/parametric_model/visual_dataframe_selector/src/main_window.py", line 111, in setup_plots
    self.data_df[self.x_axis_col], self.data_df[topic], label=topic)
  File "/home/jaeyoung/.local/lib/python3.6/site-packages/pandas/core/frame.py", line 2906, in __getitem__
    indexer = self.columns.get_loc(key)
  File "/home/jaeyoung/.local/lib/python3.6/site-packages/pandas/core/indexes/base.py", line 2900, in get_loc
    raise KeyError(key) from err
KeyError: 'u2'

Proposed Solution This PR fixes this by parsing the required actuator topic from the config directly.

ethz-asl / data-driven-dynamics

Fix interactive data selection when u2 is missing #214