Add a column to numpy 2d array

https://stackoverflow.com/questions/8486294/how-to-add-an-extra-column-to-an-numpy-array

https://stackoverflow.com/questions/36878089/python-add-a-column-to-numpy-2d-array

https://stackoverflow.com/questions/37743843/python-why-use-numpy-r-instead-of-concatenate

https://stackoverflow.com/questions/18601001/numpy-r-is-not-a-function-what-is-it

https://stackoverflow.com/questions/14468158/understanding-the-syntax-of-numpy-r-concatenation