how to select particular rows data from a array

[Larz60+]

I think you should show more on original file structure.
It seems to me there should be an easier way to do this
however this should do it for what you have

x_data_train.append([0:19], [45:64])

assuming you want the first 20 elements which are numbered 0 - 19
and 20 more beginning with the 45th.