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Slices are good for
storing collections of data, but

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the only way you can get data back out
of a slice is by using a numeric index.

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Sometimes it's useful to be able to use
other values as keys that let you look up

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items in a collection.

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Many programing languages
support collections like this.

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In C# and

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Python they're called dictionaries, in
Ruby it's a hash, in Java it's a hash map.

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Gojes seizes the term map to refer
to this sort of key value list.

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The idea is that a map maps a set
of keys to corresponding values.

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You can use any type you want as a key as
long as the keys are all the same type.

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If you know the key
a value is stored under,

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you can use the key to
retrieve that value.

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Let's create a map that stores
the names and ages of some students.

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So we're gonna specify that it
should create a new map, and

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here we specify the type that
should be used for the keys.

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Since we're using names as keys,
we're gonna use a type of string.

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And since the values will be ages,
we'll go ahead and

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use the value type of float 64.

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We'll specify that the map
should be empty when it starts.

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And we'll assign the resulting
map to the ages variable.

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Now, let's assign some values to keys
within the map, so this is just like

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the syntax for assigning to an array index
except that instead of being limited

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to numeric indexes, we can use any value
of the type we've specified for the key.

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So we can use any string we want.

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So we'll create a student with the name of
Alice and we'll say that her age is 12.

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And then we'll assign a second key, Bob.

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And we'll say that his age is nine.

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Then let's print out the whole map.

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So format, printline, ages.

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Okay let's save that.

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Try running it.

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And we see that the result is a map under
the Alice key we have an age of 12 and

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under the Bob key we have an age of 9.

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The syntax to retrieve an individual value
is just like a razor slices two except you

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use a key in place of
the numeric index again.

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So we can say format Println And

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let's print the age of Alice,
And the age of Bob.

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Save that, rerun it, and it prints
out the values for those two keys.

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Similar to arrays of slices,

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we can use a map literal to
pre-populate a map with values.

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We just type them here
within the curly braces.

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So we can say, under the key of Alice,
there should be an age of 12.

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And under the key of Bob.

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There should be an age of nine.

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Just separate the key from
the value with a colon, and

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separate multiple key
value pairs with commas.

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Let's try running this.

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And there's our populated map.

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And, as with arrays of slices,
we can use the for

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range loop to loop over each
item that a map contains.

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Each key will be assigned to
the first variable you provide.

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And each value will be assigned
to the second variable.

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So if we were to run this for range loop,

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it would print out a list of each of
the names and the corresponding ages.

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If you don't need to work with the keys

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from a map you can ignore them
by using the blank identifier.

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So for example we can print just
the ages by using the blank

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identifier in place of the keys.

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If we were to try running this,
it'll print out just the ages.

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Or if we want to ignore the values,
and use just the keys,

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we can just eliminate the second
variable that holds the values.

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So we can print just
the names with this code.

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Try running that and
we get a list of just the names.