These three operators - map, sort and grep - pack a lot of functionality. Not uncommonly, the three can be used on a single line to extract, transform and order data. Use map to initialize, distill and transform data structures. Use sort to not only order data, but also shuffle data. Finally, grep is used to extract data using a test condition. Each of these operators lends itself to idiomatic patterns, which will be discussed. As well, each of these operators can be misused and can lead to subtle bugs in your code. I'll try to point a few of these out.