I am working on a pose dataset and want to convert this data into CSV format. How to convert this data into a single row of data
You can use flatten numpy for this task. Simply convert your data to a numpy array and use the function as:

In [1]: import numpy as np                                                      

In [2]: x = [[[1,2], [3,4]]]                                                    

In [3]: x                                                                       
Out[3]: [[[1, 2], [3, 4]]]

In [4]: np.array(x).flatten()
Out[4]: array([1, 2, 3, 4])