CODEWITHSUNDEEP
matlabmatrixlogical-operators
Roger That
Roger That

Reputation: 95

Matlab logical operation on array

My question should be fairly easy, but I can't get it to work. I want to take from a matrix only the relevant rows by using logical operators and then storing those rows only. I'm used to doing this with a for-loop in other languages, but in Matlab it should be faster to run this over the entire array or matrix at once.

This is an example of what I think should work, but all my similar attempts generate different errors, and I'm not sure what to do.

Mrelevant = Matrix(Matrix.no_refs > 100)

Edit: Matrix is actually a table with headers, I want to keep only the rows that fulfil certain requirements, like the value in the column with header 'no_refs' should be above 100.

I hope this is clear enough, thanks!

Upvotes: 1

Views: 131

Answers (2)

gnovice
gnovice

Reputation: 125874

Now that you specified Matrix is a table, the answer is clear. You forgot an additional colon index argument to include all variables for the given rows you are selecting:

Mrelevant = Matrix(Matrix.no_refs > 100, :);

This will give you a new table Mrelevant that includes only those rows from Matrix where the no_refs variable is greater than 100. See here for all of the ways to access data in a table by row and/or variable.

Upvotes: 2

Scott Forsythe
Scott Forsythe

Reputation: 370

The syntax you are showing here should work, though I do not know what the purpose of the no_refs might be. The correct syntax is:

Mrelevant = matrixName(matrixName > 100)

However, this will create a single column containing the values that meet the condition. For example, 

testMatrix =
0.8147    0.0975    0.1576    0.1419    0.6557
0.9058    0.2785    0.9706    0.4218    0.0357
0.1270    0.5469    0.9572    0.9157    0.8491
0.9134    0.9575    0.4854    0.7922    0.9340
0.6324    0.9649    0.8003    0.9595    0.6787

relevant = testMatrix(testMatrix > .5)

relevant =
0.8147
0.9058
0.9134
0.6324
0.5469
0.9575
0.9649
0.9706
0.9572
0.8003
0.9157
0.7922
0.9595
0.6557
0.8491
0.9340
0.6787

However, when you say

only the relevant rows by using logical operators and then storing those rows

do you mean storing only rows where all elements in the row meet the condition? In that case, the syntax would be 

 relevant = testMatrix
 % Delete all rows that don't meet the requirement
 relevant(any(relevant<=100, 2),:) = [];

This will simply erase any row containing values that don't meet your requirement.

Upvotes: 0

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