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How can I extract non-consecutive indices from a vector?

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In 5.2 Extracting Multiple Elements, Further practice "Indices can be non-consecutive numbers. Try extracting the first, third, and sixth elements of density." How?
  14 Comments
Edward li
Edward li on 25 Aug 2023
Could someone explain the logic behind the parenthese and the brackets. like why is it in that order and what does each mean?
Voss
Voss on 19 Dec 2023
@Edward li: In this case, the parentheses are used for indexing, and the square brackets are used for array concatenation. [1,3,6] concatenates the scalars 1, 3, and 6 into a single vector, and density([1,3,6]) gets the elements of density at the indices stored in that vector.
See the Special Characters section of this page for more information:

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Accepted Answer

David Hill
David Hill on 5 Apr 2020
If you have a density array (d), then to extract the 1,3,6 elements:
extracted_elements=d([1,3,6]);
  21 Comments
Image Analyst
Image Analyst on 12 Jul 2023
@Viktoriia observe it working without commas below:
d = 10 : 10 : 60 % Sample data vector.
d = 1×6
10 20 30 40 50 60
extracted_elements = d([1 3 6]) % Get only some of the elements
extracted_elements = 1×3
10 30 60
If you execute that code on your computer what do you see? If you executed different code than above, without commas, then what was that code?
shaik mohammed ali
shaik mohammed ali on 27 May 2024 at 5:41
Edited: shaik mohammed ali on 27 May 2024 at 5:41
yes its working thank you so much

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More Answers (8)

Kakasaheb Nikam
Kakasaheb Nikam on 12 May 2020
density(3)
% extract third element
when we use [ ] square bracket, it extracting specific index position values.
so answer is
extracted_elements = density( [ 1, 3, 6 ] );

shaik sahil
shaik sahil on 22 Aug 2020
p=density([1,3,5])

Diogo Teixeira Fernandes
Diogo Teixeira Fernandes on 28 Sep 2021
extracted_elements=density([1,3,6])
it worked for me

Girish Pal
Girish Pal on 2 Sep 2020
p = density(1), density(3), density(6)
  2 Comments
Stephen23
Stephen23 on 2 Sep 2020
Edited: Stephen23 on 2 Sep 2020
While this does literally what the question requests "...extract non-consecutive indices from a vector", it only assigns the first of the comma-separated list to p, which is unlikely to give the desired effect, nor is it likely to be what the homework task requires.

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Jamal Ahmad
Jamal Ahmad on 19 Jun 2021
p=density( [ 1, 3, 6 ] )

Harish Mirji
Harish Mirji on 14 Feb 2022
density = [5 8 9 7 8 4 5 9 8 7]
density = 1×10
5 8 9 7 8 4 5 9 8 7
p = density([1 3 5])
p = 1×3
5 9 8

Ahmed
Ahmed on 7 Mar 2024
Extracting Multiple Elements
Instructions are in the task pane to the left. Complete and submit each task one at a time.
This code sets up the activity.
data = [3 0.53 4.0753 NaN;18 1.78 6.6678 2.1328;19 0.86 1.5177 3.6852;20 1.6 3.6375 8.5389;21 3 4.7243 10.157;23 6.11 9.0698 2.8739;38 2.54 5.30023 4.4508]
data = 7×4
3.0000 0.5300 4.0753 NaN 18.0000 1.7800 6.6678 2.1328 19.0000 0.8600 1.5177 3.6852 20.0000 1.6000 3.6375 8.5389 21.0000 3.0000 4.7243 10.1570 23.0000 6.1100 9.0698 2.8739 38.0000 2.5400 5.3002 4.4508
density = data(:,2)
density = 7×1
0.5300 1.7800 0.8600 1.6000 3.0000 6.1100 2.5400
x = density([1,3,6])
x = 3×1
0.5300 0.8600 6.1100

Parvin
Parvin on 14 Mar 2024
This code sets up the activity.
data = [3 0.53 4.0753 NaN;18 1.78 6.6678 2.1328;19 0.86 1.5177 3.6852;20 1.6 3.6375 8.5389;21 3 4.7243 10.157;23 6.11 9.0698 2.8739;38 2.54 5.30023 4.4508]
data = 7×4
3.0000 0.5300 4.0753 NaN 18.0000 1.7800 6.6678 2.1328 19.0000 0.8600 1.5177 3.6852 20.0000 1.6000 3.6375 8.5389 21.0000 3.0000 4.7243 10.1570 23.0000 6.1100 9.0698 2.8739 38.0000 2.5400 5.3002 4.4508
To extract the first, third, and sixth elements of density, use [1 3 6] as an index.
density = [1 3 6]
density = 1×3
1 3 6
data(density)
ans = 1×3
3 19 23

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