To expand on your #2: I work with a lot of traders. One antipattern I noticed is that when there's a problem with the data, they'll do all sorts of permutatio

To expand on your #2: I work with a lot of traders. One antipattern I noticed is that when there's a problem with the data, they'll do all sorts of permutations and aggregations and then scratch their chins and ponder about it for hours. Go to the fucking source and find an example of the problem! Read it line by line, usually it will be obvious what happened. Corollary: Don't assume your data is correct, most outliers ina large data set are problems with the data itself. Build a few columns that serve as sanity checks. One good example is a column that shows the distance between this sequence number and the last, anything >1 is a dropped message.