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Multidimensional arrays are a special type of array. They're different than jagged arrays and they have a special syntax in C#. Let's explore how they're different.
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In the previous video we saw one way
to create a spreadsheet by creating
0:00
nested arrays.
0:05
This is called a jagged array and
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it works great when we want the inner
arrays to be different lengths.
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This is a common scenario for
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example think about a school's
class rules the outer rows.
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The outer array contains the classrooms,
and
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the inner arrays contain
the students in each classroom.
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Each classroom may have
a different number of students.
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However, sometimes we don't need nor
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want the sizes of the inner
arrays to be different lengths.
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These are true two dimensional arrays.
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In the spreadsheet example this would mean
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that every row in a spreadsheet has
exactly the same number of cells.
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We create a two dimensional array similar
to the way a jagged array is created.
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So I'll say cell open square bracket
comma closing square bracket sheet
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equals new cell and here we can put the
dimensions of our two dimensional array.
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So I'll say it has 100 rows and
10 columns.
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Instead of two sets of angle brackets,
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instead we have a single set of
angle brackets with a comma in it.
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On the right side we put both dimensions
of the array at the same time.
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This is more than syntactic sugar.
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This is actually a single
array of 1,000 items.
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They're organized into dimensions,
one for rows and the second for columns.
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If we get the value of the arrays length
property we see that it has 1,000 items.
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Remember that the length of
the jagged array of arrays was 100.
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Instead this is giving us the total
number of items in the array.
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The C# Repl and Mono doesn't know how to
print out a multi dimensional array like
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this, but we can see where individual
items of the array are alike so
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just say sheet first index and
then the second index.
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And here we see that the element
at index 0,0 is nil.
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Just like with jagged arrays,
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the elements are initialized
to their types default value.
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In the case of the cell class this is nil.
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We still need to assign objects
to each index of the array.
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Again we'll need nested loops for this.
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So I'll say for int rowIndex
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starting at 0 while row
index is less than sheet.
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Now here instead of saying length we're
going to use the GetLength method and
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here we'll pass the dimension of the array
that we'd like to get the length for.
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So I'll enter in zero to
get the first dimension.
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And now I'll just say rowIndex++.
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Now to loop through all the columns,
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I'll say four int colIndex starting
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at 0 colIndex less than
sheet.GetLength and
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you'll pass in 1 to get the length
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of the second dimension and
then colIndex ++.
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Now here we'll say sheet rowIndex,
colIndex and
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set each item in the array
equal to a new Cell.
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Now all of the indexes in the array
have been set to an instance of cell.
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We can check it out by just saying sheet
and let's get the item index 2, 3.
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Unlike with jagged arrays,
we can't use nested for
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each loops to print out
the entire spreadsheet.
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For each loop work with jagged arrays
because they're arrays of other arrays.
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A multi dimensional array is actually just
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one large array that's subdivided
into equal sized parts.
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There are no inner arrays to loop through.
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So we can't do something like
foreach Cell row in sheet.
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This wouldn't work.
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Instead to loop through a multi
dimensional array we nest the for
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loops just like we did up here.
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Only instead of setting the values
here we can do anything we want,
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such as print them out.
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As you can see jagged arrays are more
flexible than multidimensional arrays.
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So you'll find that jagged
arrays are more common.
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However, multidimensional arrays
are useful in many scenarios.
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One nice thing about multi dimensional
arrays is that we can initialize
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both dimensions at once
to their default values.
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For example an array of integers like so
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where I can say int[,]
matrix = new int and
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then create a matrix with five rows and
five columns.
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Now every value in the matrix
is initialized to zero.
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Matrices like this are used a lot
in computer science, mathematics,
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computer graphics and many other fields.
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In most cases, you'll find that nested
arrays like jagged arrays and other types
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of nested collections, are much more
common than multi dimensional arrays.
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So far,
as we've been creating in our spreadsheet
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we've only seen examples of
arrays with rows and columns.
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This is only two dimensions.
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We can create arrays with three or
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more dimensions in the same
way we do with two dimensions.
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One scenario for a three
dimensional array is a spreadsheet,
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where each cell can
contain multiple values.
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in the case of jagged arrays we just have
three sets of square brackets like this.
5:58
Again with Jagged arrays we still need
to instantiate both of these inner
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dimensions here.
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I'll leave this as an exercise for you.
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Since we have three
nested arrays we'll need
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three nested loops to initialize them.
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With multidimensional arrays,
we can just add more columns.
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So I can say int and then two commas
here to create three dimensions,
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and I'll call this
a threeDimMatrix that's equal
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to a new integer array of size five and
5,5.
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Multi dimensional arrays can
have a maximum of 32 dimensions.
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Unless you're doing quantum physics of
some sort, it's unlikely that you'll ever
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need to deal with a multidimensional array
with more than three dimensions though.
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Jagged arrays can have as many
nested arrays as we'd like.
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We can even combine jagged and
multidimensional arrays like this.
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I'll say int, so this is an integer array
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of a three dimensional multidimensional
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array of a single dimension array and
I'll call it yikes.
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So this would be an array of
five three-dimensional arrays of
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integer arrays.
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Now we're just talking craziness though.
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