meet it

Count with a dictionary, then visit every pair.

A counts how often each thing turns up. Go through the items one by one. If the dictionary already has the item as a key, add one to its value with ++. If not, start it at 1.

foreach (var pair in tally) visits every pair in turn. Each pair is a with two parts: pair.Key and pair.Value.

A plain Dictionary makes no promise about order, so its pairs might come out any way round. A works the same but keeps its keys sorted, so a loop visits them from A to Z.

using System;
using System.Collections.Generic;

string[] votes = { "pizza", "tacos", "pizza", "sushi", "pizza" };
var tally = new SortedDictionary<string, int>();
foreach (string vote in votes)
{
    if (tally.ContainsKey(vote))
    {
        tally[vote]++;
    }
    else
    {
        tally[vote] = 1;
    }
}
foreach (var pair in tally)
{
    Console.WriteLine($"{pair.Key}: {pair.Value}");
}

Whenever the order of the output matters, reach for a SortedDictionary.

guess first

The dice have been rolling. What will this show?

Guess before you run it. Wrong guesses are how you learn, and nothing is marked.

using System;
using System.Collections.Generic;

string[] rolls = { "six", "two", "six", "six", "four" };
var count = new SortedDictionary<string, int>();
foreach (string roll in rolls)
{
    if (count.ContainsKey(roll))
    {
        count[roll]++;
    }
    else
    {
        count[roll] = 1;
    }
}
foreach (var pair in count)
{
    Console.Write($"{pair.Key}={pair.Value} ");
}

your turn

Your turn. Count the cars going past.

Add two more car colours on line 4. Then finish line 19 so each line shows the colour, a colon and its count, like red: 2.

Your code

output

press run to see what happens

fix it

The café tally crashes on the first order. Fix it!

Broken code to fix

output

press run to see what happens

C# stops with KeyNotFoundException on line 8. What is in tally the first time it meets a latte?
++ needs a value to add one to, and a brand new key has none yet.
Wrap line 8 in if (tally.ContainsKey(order)), with an else block that sets tally[order] = 1;.

nailed it

you can tally anything. :D

A tally adds one to a key, or starts it at 1.
Each pair in a loop has a Key and a Value.
A SortedDictionary keeps its keys in order.

new words in your collection

tally
KeyValuePair
SortedDictionary

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