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1. Slicing2. Diminution3. Augmentation

ArraysCommon Opeartions

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ARRAY SLICINGAccessing more than one element of an array

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Array SlicingIn general, a slice is a "smaller piece" of something. The

range operator is frequently used when getting a slice.

% Copy all elements in rows 1 and 2, % columns 1 through 4

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…

… …

Array SlicingIn general, a slice is a "smaller piece" of something. The

range operator is frequently used when getting a slice.

% Copy all elements in rows 1 and 2,% columns 1 through 4M1 = M(___ ,____);

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Array SlicingIn general, a slice is a "smaller piece" of something. The

range operator is frequently used when getting a slice.

% Copy all elements in rows 1 and 2,% columns 1 through 4M1 = M(1:2 ,____);

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Array SlicingIn general, a slice is a "smaller piece" of something. The

range operator is frequently used when getting a slice.

% Copy all elements in rows 1 and 2,% columns 1 through 4M1 = M(1:2 ,____);

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Array SlicingIn general, a slice is a "smaller piece" of something. The

range operator is frequently used when getting a slice.

% Copy all elements in rows 1 and 2,% columns 1 through 4M1 = M(1:2,1:4);

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Array SlicingIn general, a slice is a "smaller piece" of something. The

range operator is frequently used when getting a slice.

% Copy all elements in rows 1 and 2% that are in columns 1 through 4M1 = M(1:2, 1:4);

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Array SlicingIn general, a slice is a "smaller piece" of something. The

range operator is frequently used when getting a slice.

% Copy all elements in rows 1 and 2% that are in columns 1 through 4M1 = M(1:2, 1:4);

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Real-life #1: Eliminating bad data In wind tunnels, the data is

obtained throughout the tunnel.

However, data is usually flawed around the walls, or far away form the object itself.

Given an array of pressure/temperature/or density obtained, only the ones far from the wall are kept for analysis!

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Real-life #1: Eliminating bad data In wind tunnels, the data is

obtained throughout the tunnel.

However, data is usually flawed around the walls, or far away form the object itself.

Given an array of pressure/temperature/or density obtained, only the ones far from the wall are kept for analysis!

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ARRAY DIMINUTION

Making arrays smallerDeleting an element, a row, a column, etc..

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Pronounce:“Dim’ – min – yoo’ – shun”

Array Diminution To eliminate the whole content, re-define it as an empty-

vector:scores = []; %delete all scores

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Array Diminution To eliminate the whole content, re-define it as an empty-

vector:scores = []; %delete all scores

To eliminate a single value from a vector, either take a slice:

HighScores = [757, 65, -13, -89];HighScores = HighScores(1:3); %deletes last

%score

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Array Diminution To eliminate the whole content, re-define it as an empty-

vector:scores = []; %delete all scores

To eliminate a single value from a vector, either take a slice:

HighScores = [757, 65, -13, -89];HighScores = HighScores(1:3); %deletes last

%score

Or use the empty-vector:HighScores(4) = []; %removes 4th score

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Example Diminution After analyzing data, get rid of some data: in this case, assign the

empty brackets []

For example, get rid of the number 8 in b below:

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This action changes the original vector and cannot be undone.

Example Diminution After analyzing data, get rid of some data: in this case, assign the

empty brackets []

For example, get rid of the number 8 in b below:

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This action changes the original vector and cannot be undone.

Array Diminution, cont. To eliminate an entire row/column:

1. Use the range operator, combined with2. the empty-vector

M = [1, 2, 3; 4, 5, 6];M(:, 1) = [] … Read it as:

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%”M

Array Diminution, cont. To eliminate an entire row/column:

1. Use the range operator, combined with2. the empty-vector

M = [1, 2, 3; 4, 5, 6];M(:, 1) = [] … Read it as:

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%”M , all-rows

Array Diminution, cont. To eliminate an entire row/column:

1. Use the range operator, combined with2. the empty-vector

M = [1, 2, 3; 4, 5, 6];M(:, 1) = [] … Read it as:

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%”M , all-rows, 1stcolumn

Array Diminution, cont. To eliminate an entire row/column:

1. Use the range operator, combined with2. the empty-vector

M = [1, 2, 3; 4, 5, 6];M(:, 1) = [] … Read it as:

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%”M , all-rows, 1stcolumn , delete!”

Array Diminution, cont.Question:

Can we eliminate a single value from a matrix?

M = [1, 2, 3; 4, 5, 6];M(2, 2) = [] <enter>

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Array Diminution, cont.Question:

Can we eliminate a single value from a matrix?

M = [1, 2, 3; 4, 5, 6];M(2, 2) = [] <enter>

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No – because that would mean some rows or columns would have more values than others.

Real life#2 – similar example

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Clearly, bad results on the walls…

Real life#2 – similar example

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Real life#2 – similar example

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Real life#2 – similar example

Suppose you want to delete the top now, since that is also a wall in the wind tunnel. What would be the command line?____________________________________

AUGMENTING AN ARRAYInsert values at the end of an array (not in the middle, nor beginning)

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Array Augmentation, reviewAugmentation = “Adding to” = making an array bigger. For example:V = [1, 2, 3];

To augment more columns, it’s much like doing a running total or running product: to the current variable, perform an action:

V = [V, 4, 5, 6]; Result: [ _________________ ] ?

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Array Augmentation, reviewAugmentation = “Adding to” = making an array bigger. For example:V = [1, 2, 3];

To augment more columns, it’s much like doing a running total or running product: to the current variable, perform an action:

V = [V, 4, 5, 6];

To augment with another row vector variable:V1 = [3, 4, 5];V2 = [6, 7, 8];V1 = [V1; V2];

Makes a matrix!

Result: [ _________________ ] ?

Result:__ __ __. __ __ __.

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Array Augmentation, reviewAugmentation = “Adding to” = making an array bigger. For example:V = [1, 2, 3];

To augment more columns, it’s much like doing a running total or running product: to the current variable, perform an action:

V = [V, 4, 5, 6];

To augment with another row vector variable:V1 = [3, 4, 5];V2 = [6, 7, 8];V1 = [V1; V2];

To augment with a column vector variable:V1 = [6; 8; 9];V2 = [10; 20; 30];V1 = [V1, V2];

Makes a matrix!

Why use a comma? ________________

Result: [ _________________ ] ?

Result:__ __ __. __ __ __.

Result:__ __ .

__ __ __ __

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Array Augmentation, review Works for matrices, too:

M1 = [1, 2, 3; 4, 5, 6]; %original matrixM1 = [M1; 7, 8, 9]; % attach a row to M1M1 = [M1, [11, 2, 33; 44, 33, 22; 1, 0, 2]]

M1 =

1 2 3 11 2 33 4 5 6 44 33 22 7 8 9 1 0 2

Be sure to augment with the correct number of rows / columns!

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Extending an array

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Array b does not have 4 columns… mmm… what will it do?

Extending an array

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Fills in with zerossss.

Wrapping Up Vocabulary: slicing, range operator, diminution, empty

vector, empty brackets, augmentation To slice means to refer to a piece of an array

To copy their values, to replace their values, to delete their values, etc…

Use the : operator to refer to ALL rows or ALL columns. To diminute an array is to reduce its size

Use empty brackets Feasible as long as dimension-wise, it makes sense!

To augment an array is to 'add on values' Only at the beginning or end, not in the middle. Use [ ] as if creating arrays, use the variable inside the [ ] as

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