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data in files and arrays

Sorting is easier in memory

If you are writing a program that is going to deal with a lot of data, you
need to decide where you need to keep that data while the program works
with it. Most of the time, you will have two choices:

1 Keep the data in files on the disk.
If you have a very large amount of data, the obvious place to put it is on
disk. Computers can store far more data on disk than they can in memory.
Disk storage is persistent: if you yank the power cord, the computer
doesn’t forget the information written on the disk. But there is one real
problem with manipulating data on disk: it can be very slow.

2 Keep the data in memory.
Data is much quicker to access and change if it’s stored in the computer’s
memory. But, it’s not persistent: data in memory disappears when your
program exits, or when the computer is switched off (unless you remember
to save it to a file, in which case it becomes persistent).

Keep the data in memory
You have lots of lines of
If you want to sort a lot of data, you will need to shuffle data around data, so you'll need lots of
quite a lot. This is much faster in memory than on disk. variables... right?!?
Of course, before you sort the data, you need to read it into memory,
perhaps into a large number of individual variables:

You need to move
the lines of data
in the results.txt
file into memory
before trying to
sort it.

Do you have a big
cupboard?!? Because that's
You are going to have a problem if you attempt to move all those a lot of jars...
lines of data into the computer‛s memory. What type of problem do
you think you‛ll have?

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