How to separate a vector into two different vectors?
21 views (last 30 days)
Show older comments
Kristin Aldridge
on 2 Dec 2021
Commented: Star Strider
on 2 Dec 2021
I have a vector named "age_vec" that I would like to piece into two groups, those above 37.5 and those below, and place those numbers into another vector. I keep trying to run this through a for loop but it puts all the numbers in the same vector, either all placed in agegreater or ageless, or I even tried just getting it to count those above and those below and it keeps putting everything into just one vector/variable.
Thank you.
age_vec =[ 21 18 57 52 20 22 23 21.50 38 31 30 29 58 53 21.75 86 55]
%Counting those above and those below
ageless=0;
agemore=0;
for i=1:length(age_vec)
if age_vec > 37.5
ageless= ageless + 1
else agemore= agemore + 1
end
end
%Placing into vectors
ageless=[];
agemore=[];
for i=1:length(age_vec)
if age_vec < 37.5
ageless=[ageless age_vec] + 1
else agemore=[agemore age_vec] + 1
end
end
0 Comments
Accepted Answer
Star Strider
on 2 Dec 2021
Try this —
age_vec =[ 21 18 57 52 20 22 23 21.50 38 31 30 29 58 53 21.75 86 55];
Lv = age_vec > 37.5; % Logical Vector
age_more = age_vec(Lv)
age_less = age_vec(~Lv)
.
2 Comments
More Answers (3)
Image Analyst
on 2 Dec 2021
Edited: Image Analyst
on 2 Dec 2021
Try this:
age_vec =[ 21 18 57 52 20 22 23 21.50 38 31 30 29 58 53 21.75 86 55]
% Find indexes that are more than 37.5
moreIndexes = age_vec > 37.5
% Extract into two new vectors.
ageless=age_vec(~moreIndexes)
agemore=age_vec(moreIndexes)
0 Comments
Voss
on 2 Dec 2021
Probably the easiest way to do what you want is to use logical indexing. First make a vector of logicals that say whether each element of age_vec is greater than 37.5 or not:
is_greater = age_vec > 37.5;
Then make two new vectors by separating the elements of age_vec according to the corresponding value in is_greater:
age_more = age_vec(is_greater);
age_less = age_vec(~is_greater);
If you really want or need to use a for loop, let me know and I can show you how that would work, but this way with logical indexing is much more concise.
0 Comments
James Tursa
on 2 Dec 2021
Edited: James Tursa
on 2 Dec 2021
Others have already pointed out better ways of doing this. But to answer your question as to why your current code is not working, it is because you need to use the index i in your code. E.g.,
if age_vec(i) < 37.5
ageless = [ageless age_vec(i)];
else
agemore = [agemore age_vec(i)];
end
This will incrementally build up the ageless and agemore vectors, but at each iteration you will have to deep copy one of the vectors, so the performance will be severly impacted as the size of age_vec gets large. Hence the desire to use a different method as others have suggested.
0 Comments
See Also
Categories
Find more on Matrix Indexing in Help Center and File Exchange
Products
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!