Removing large parts of an array

I have an array that has around 8000 elements. I wish to delete the last 7000 in a simple way, so that I am left with an array that has just the first 1000. Is there any way to do this?

[Rik]

Is this homework?

[Stefan Ganescu]

No, I have an 8000Hz signal in matlab and i wish to only show the first part so that it is easier to read

Answer 1

[Voss]

If it is a row or column vector:

x = randn(1,8000);
size(x)

ans = 1×2

1 8000

last_n_to_remove = 7000;

x(end-last_n_to_remove+1:end) = [];

size(x)

ans = 1×2

1 1000

[Stefan Ganescu]

Thank you! Though with "end-last_n_to_remove+1" it only has 998 elements, so I think it's meant to be -1.

[Voss]

You're welcome!

You can see in my answer that x had 1000 elements after removing some using

x(end-last_n_to_remove+1:end) = []

Maybe you put parentheses somewhere where I didn't have them? I.e.:

 x(end-(last_n_to_remove+1):end) = [];

or, equivalently, stored last_n_to_remove+1 in a variable and used that?

With parentheses:

x = randn(1,8000);
last_n_to_remove = 7000;
x(end-(last_n_to_remove+1):end) = [];
size(x)

ans = 1×2

1 998

x = randn(1,8000);
last_n_to_remove = 7000;
x(end-(last_n_to_remove-1):end) = [];
size(x)

ans = 1×2

1 1000

Without parentheses:

x = randn(1,8000);
last_n_to_remove = 7000;
x(end-last_n_to_remove+1:end) = [];
size(x)

ans = 1×2

1 1000

[Stefan Ganescu]

Ah, you're right - I skipped having a variable and just wrote "end-7001:end" but it needed to be a variable to work correctly with +1

[Voss]

Ah, I see. Ordinarily I would write

x(end-6999:end) = [];

But I decided to make it a variable in order to try to be clear why it's 6999 and not 7000 (which is because the last element is end=end-0).

[Stefan Ganescu]

If there is a way to show the first X elements, is there also a way to show the last X or elements between 2 values? Like if i wanted to show elements 3000 through 4000.

[Voss]

x = 1:8000;

% show the first 100 elements:
x(1:100)

ans = 1×100

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

% show the last 100 elements:
x(end-99:end)

ans = 1×100

7901 7902 7903 7904 7905 7906 7907 7908 7909 7910 7911 7912 7913 7914 7915 7916 7917 7918 7919 7920 7921 7922 7923 7924 7925 7926 7927 7928 7929 7930

% show elements 3000 to 4000:
x(3000:4000)

ans = 1×1001

3000 3001 3002 3003 3004 3005 3006 3007 3008 3009 3010 3011 3012 3013 3014 3015 3016 3017 3018 3019 3020 3021 3022 3023 3024 3025 3026 3027 3028 3029

(when you do this on your computer, your command line will show the entire 100 or 1001 elements or whatever)