title: Convert list of lists with different lengths to a numpy array
body: <p>I have list of lists with different lengths (e.g. <code>[[1, 2, 3], [4, 5], [6, 7, 8, 9]]</code>) and want to convert it into a <code>numpy</code> array of integers. I understand that 'sub' arrays in <code>numpy</code> multidimensional array must be the same length. So what is the most efficient way to convert such a list as in example above into a <code>numpy</code> array like this <code>[[1, 2, 3, 0], [4, 5, 0, 0], [6, 7, 8, 9]]</code>, i.e. completed with zeros?</p>