This is my favorite MySQL hack. This is how you emulate the lag function: SET @quot=-1; select time,company,@quot lag_quote, @quot:=quote curr_quote from stocks order by company,time; lag_quote holds the value of previous row’s quote. For the first row @quot is -1. curr_quote holds the value of current row’s quote. Notes: order by clause is important … Read more
You can do a vectorized sliding window in numpy using fancy indexing. >>> import numpy as np >>> a = np.array([[00,01], [10,11], [20,21], [30,31], [40,41], [50,51]]) >>> a array([[ 0, 1], [10, 11], [20, 21], #define our 2d numpy array [30, 31], [40, 41], [50, 51]]) >>> a = a.flatten() >>> a array([ 0, 1, … Read more
I think of it as more a technique than an algorithm. It’s a technique that could be utilized in various algorithms. I think the technique is best understood with the following example. Imagine we have this array: [ 5, 7, 1, 4, 3, 6, 2, 9, 2 ] How would we find the largest sum … Read more