Part 5

Each and Key

Each

1. Write the function Backwards which accepts a nested vector of character vectors as its argument and reverses both the order of elements and the contents of each vector within.

         Backwards 'reverse' 'these' 'words'
   ┌─────┬─────┬───────┐
   │sdrow│eseht│esrever│
   └─────┴─────┴───────┘
   

2. Write the function SizeSort which sorts its nested vector argument according to the length of each subvector

         SizeSort 'how' 'will' 'we' 'sort' 'these' 'words?'
   ┌──┬───┬────┬────┬─────┬──────┐
   │we│how│will│sort│these│words?│
   └──┴───┴────┴────┴─────┴──────┘
         SizeSort (1 2)(3 1 4 1 5)5(5 4 3)5
   ┌─┬─┬───┬─────┬─────────┐
   │5│5│1 2│5 4 3│3 1 4 1 5│
   └─┴─┴───┴─────┴─────────┘
   

3. Create the variable nest which has the following properties:

         ⍴nest
   2 3
         ≡nest
   ¯2
         ⍴¨nest
   ┌─┬┬─┐
   │ ││2│
   ├─┼┼─┤
   │3││6│
   └─┴┴─┘
         ]display ∊nest
   ┌→───────────────────┐
   │I 3 am 1 5 8 amatrix│
   └+───────────────────┘
         ⍴∊nest
   14
   

Visit to the museum

Here are some data and questions about visits to a museum.

The section_names are the names of each of the four sections in the museum.

section_names ← 'Bugs' 'Art' 'Fossils' 'Sea Life'

The visits table represents 1000 visits to museum sections over a four week period. The four columns represent:

• The section that was visited as an index into the section_names
• The day of the visit in Dyalog Date Number format.
• The arrival time in minutes from midnight. For example, 15:30 is 930 minutes.
• The departure time in minutes from midnight.

⎕RL←42 ⋄ days←43589+?1000⍴28 ⋄ (arr lïv)←539+?2⍴⊂1000⍴510 ⋄ section←?1000⍴4
visits←(⊂⍋days)⌷section,days,(⊂∘⍋⌷⊢)⍤1⍉↑arr lïv

1. How many visitors arrived before 10AM?
2. How many visitors arrived between 11AM and 3PM?
3. What was the most popular section by visit duration?