Slicing and dicing a list
There are many times when we want to pick items from a list. One of the most common kinds of processing is to treat the first item of a list as a special case. This leads to a kind of head-tail processing where we treat the head of a list differently from the items in the tail of a list.
We can use these techniques to make a copy of a list, also.
Getting ready
We have a spreadsheet that was used to record fuel consumption on a large sailboat. It has rows which look like this:
date | engine on | fuel height |
engine off | ||
Other notes | ||
10/25/2013 | 08:24 | 29 |
13:15 | 27 | |
calm seas—anchor solomon's island | ||
10/26/2013 | 09:12 | 27 |
18:25 | 22 | |
choppy—anchor in jackson's creek |
Fuel height? Yes. There's no float sensor to estimate the level of fuel in the tanks. Instead there's a sight-gauge that allows direct observation of the fuel. It's calibrated in inches of depth. For all practical purposes the tank is rectangular, so the depth shown can be converted to volume pretty easily—31 inches of depth is about 75 gallons...
