How do we deal with CSV files? Luckily, the loadtxt() function can conveniently read CSV files, split up the fields, and load the data into NumPy arrays. In the following example, we will load historical stock price data for Apple (the company, not the fruit). The data is in CSV format and is part of the code bundle for this book. The first column contains a symbol that identifies the stock. In our case, it is AAPL. Second is the date in dd-mm-yyyy format. The third column is empty. Then, in order, we have the open, high, low, and close price. Last, but not least, is the trading volume of the day. This is what a line looks like:

AAPL,28-01-2011, ,344.17,344.4,333.53,336.1,21144800

For now, we are only interested in the close price and volume. In the preceding sample, that will be 336.1 and 21144800. Store the close price and volume in two arrays as follows:

c,v=np.loadtxt('data.csv', delimiter=',', usecols=(6,7), unpack=True)

As you can see, data is...