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How do I select and/or delete values of a certain index in an array?

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Emily22
Emily22 2017-4-7
回答： Image Analyst 2017-4-7
I have a data set (OrbSolPwr) in a 2880 x 1 double array. I only want the first (n) terms. How do I either select the first (n) terms into a new array or delete the (n+1):numel(OrbSolPwr) terms? (Using the R2016a student/academic version)
n = 1261;
m = numel(OrbSolPwr); % m = 2880
for i = 1:m;
if i > n:
OrbSolPwr(i,1) = [];
end
end
First try gives the error that a null assignment can have only one con-colon index for line 5 above. I realize that the index would also get messed up since the length will change as the data set shrinks, but I don't know how to write that.
n = 1261;
m = numel(OrbSolPwr); % m = 2880
for i = n+1:m;
OrbSolPwr(i,1) = [];
end
I also tried this, which gives the same error as before.

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采纳的回答

Nick
Nick 2017-4-7
编辑：Nick 2017-4-7
This is how you would extract the data to a new array
%Generate random numbers for Example
OrbSolPwr = randi(10,2880,1);
%Select cutoff
n = 15;
newOrbSolPwr = zeros(n,1);
%Extract values from old data to new data
for i = 1:n
newOrbSolPwr(i) = OrbSolPwr(i);
end
if you wanted to delete the elements. The index will keep shrinking but its ok because we are iterating by a negative 1 so it won't exceed the matrix dimensions
m = numel(OrbSolPwr)
for i = m:-1:n+1
OrbSolPwr(i) = [];
end

更多回答（1 个）

Image Analyst
Image Analyst 2017-4-7
Nick's solution is like what you'd do in C or Java, not MATLAB. In MATLAB, you simply do it in one line of code by extracting the rows you want:
OrbSolPwr = OrbSolPwr(1:n);
Any elements after n are discarded. No for loop is needed at all because MATLAB is a vectorized language.

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