# matlab logical array indexing

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For example, consider the 4-by-4 magic square A: Find the treasures in MATLAB Central and discover how the community can help you! Pick out the odd-numbered elements of a numeric matrix. Ideally the Code would look like this: The values in C and D to be used in the equation have to be in the same row and column as in A. You can also select a web site from the following list: Select the China site (in Chinese or English) for best site performance. Learn more about arrays, indexing, floating point, binary floating point numbers A logical matrix provides a different type of array indexing in MATLAB. To replace all NaN elements of the matrix B with zero, use. D is an 5x4 array. Based on your location, we recommend that you select: . It is possible that creating a large logical array via logical indexing could be slower than a loop. In this masking type of operation, every true element in the indexing array is treated as a positional index into the array being accessed. Logical â¦ Logical indexing is always just "selected, or not selected" and so always works in linear indexing order, so trying to use logical indexing with [3 2 1] or other non-decreasing order is going to fail unless you take additional steps. By testing your code ít does not seem that way. MathWorks is the leading developer of mathematical computing software for engineers and scientists. Array Indexing Logical Values. With two for-loops it would look like this: I'm not sure if the same can be achieved with logical indexing as C(B) just gives a vector as an output and of course then the dimensions do not agree. This does indeed work, but it seems that I do not fully understand how the logical indexing is working. Cell Arrays and Indexing?. If C and D are matrices, then C(D) is a logical indexing expression if C and D are the same size, and D is a logical matrix. https://www.mathworks.com/matlabcentral/answers/678563-manipulating-values-in-an-array-with-logical-indexing#answer_565493, https://www.mathworks.com/matlabcentral/answers/678563-manipulating-values-in-an-array-with-logical-indexing#comment_1183743, https://www.mathworks.com/matlabcentral/answers/678563-manipulating-values-in-an-array-with-logical-indexing#comment_1183803, https://www.mathworks.com/matlabcentral/answers/678563-manipulating-values-in-an-array-with-logical-indexing#comment_1183848, https://www.mathworks.com/matlabcentral/answers/678563-manipulating-values-in-an-array-with-logical-indexing#comment_1183983, https://www.mathworks.com/matlabcentral/answers/678563-manipulating-values-in-an-array-with-logical-indexing#comment_1184983, https://www.mathworks.com/matlabcentral/answers/678563-manipulating-values-in-an-array-with-logical-indexing#comment_1184988, https://www.mathworks.com/matlabcentral/answers/678563-manipulating-values-in-an-array-with-logical-indexing#answer_565483, https://www.mathworks.com/matlabcentral/answers/678563-manipulating-values-in-an-array-with-logical-indexing#comment_1183748. Determine if input is logical array; returns true if A is a logical array and false otherwise. Logical Indexing Example 1. Every technique that uses logical matrices as indexing of the entire array is going to have the same problem of being insensitive to order of the panes. What does confuse me is the fact that the following code does work as well: In this case the output of C(B) and D(B) is, e.g., a 10x1 Array, it is transposed to the Array in your code. When you want to access selected elements of an array, use indexing. Learn more about cell arrays, indexing . Here is an example of value-based indexing where array B 7indexes into elements 1, 3, 6, , and 10 of array A. Logical Indexing. When we index an array with a logical variable, Matlab is using find to locate all the true elements and convert them to indices. Learn more about matlab, cell arrays MATLAB https://www.mathworks.com/matlabcentral/answers/307310-logical-indexing-in-cell-array#answer_238996, https://www.mathworks.com/matlabcentral/answers/307310-logical-indexing-in-cell-array#answer_238984, https://www.mathworks.com/matlabcentral/answers/307310-logical-indexing-in-cell-array#comment_398680, https://www.mathworks.com/matlabcentral/answers/307310-logical-indexing-in-cell-array#answer_238983, https://www.mathworks.com/matlabcentral/answers/307310-logical-indexing-in-cell-array#comment_398682. The array has logical 1 ( true) values where A is odd. Which values are changed is decided by a logical array 10x10 Array B. works perfectly. Indexing can be classified considering the following two attributes. 0. Let's talk about the basic rules of logical indexing, and then we'll reexamine the expression B(isnan(B)). Another type of array index, a logical index, designates the elements of A based on their position in the indexing array, B. Logical indexing in cell array. Logical Indexing. For example, A (A > 12) extracts all the elements of A that are greater than 12. While most indices are numeric, indicating a certain row or column number, logical indices are positional. I tried reshaping the vectors as a matrix, but this only works if there arent any "holes" in the logical Matrix B. The array logInd is not an array of double numbers, but have the class logical. Logical indexing of cell array. Learn more about logical indexing, matrix array, vectorization But amongst other things this depends on the actual size of your arrays, which we don't know. Choose a web site to get translated content where available and see local events and offers. Thank you for posting the amplification and clarification! Create a numeric matrix. Introduction to MATLAB Indexing. A video segment from the upcoming Coursera MOOC on introductory computer programming with MATLAB by Vanderbilt. MATLAB supports a type of array indexing that uses one array as the index into another array. The correct values are replaced in the correct locations. 0 â® Vote. In logical indexing, you use a single, logical array for the matrix subscript. Many MATLAB functions that start with is return logical arrays and are very useful for logical indexing. You may receive emails, depending on your. Unable to complete the action because of changes made to the page. For example, you could replace all the NaN elements in an array with another value by using a combination of isnan, logical indexing, and scalar expansion. 1. The output is always in the form of a column vector. Logical Indexing of Cell Array containing matrices. Logical indexing will allow us to select and manipulate only those subsets of data that satisfy particular logical conditions. Logical indexing of cell array. In MATLAB®, there are three primary approaches to accessing array elements based on their location (index) in the array. Learn more about cells, cell arrays, for loops Select Rows with Logical Indexing. Is there a way to search strings in a cell array similar to numeric arrays? This code returns logical true for when both cells are 0 or 1. Well, with this example we say goodbye to logical indexing. The individual indices are sometimes referred to as subscripts in Matlab documentation (see for example sub2ind). Learn more about using logical arrays to change specific positions in a muiltidimensional array Logical indexing is a powerful MATLAB feature that can save you from writing many loops. 22: true. The result of the expression is an array of logical indices. Reload the page to see its updated state. It also returns true if A is an instance of a class that is derived from the logical class. We also don't know what your system specifications are. MATLAB provides us with plenty of functionalities, useful in various computational problems. Assigning elements in a vector using a logical array follows the linear indexing convention. The array C is initalized as a 1x20something Array depending on B. In this article, we will study a powerful MATLAB functionality called âMATLAB Indexingâ. These approaches are â¦ Find the treasures in MATLAB Central and discover how the community can help you! An intermediate situation exists, which may be termed partially linear indexing: 1.1. Indexing is the way to select a particular element in an array. Sign in to comment. Follow 36 views (last 30 days) James Metz on 4 Apr 2020. If you are trying to calculate something like the following: As the above equation is only false for the first column, the logical Matrix B looks like this. I was thinking that by using logical indexing the programm is just ignoring the values where the condition is not fulfilled. 1.â¦ If you want to make it work the code has to look like this: I guess the colon does indicate that linear indexing should be used, which does agree with the logical array. By themselves, logical vectors are not that exciting, and in fact you will probably very rarely view all the elements in a logical vector like this. That means that i only want to change the values of A(:,2:5). Every variable in MATLAB® is an array that can hold many numbers. The only significant change I made is to use element-wise exponentiation (. Vote. Suppose I do know that the first column of B, my logical array, is zero. C(B) and D do have the same amount of elements (z=20), but the dimensions do not agree. You can also select a web site from the following list: Select the China site (in Chinese or English) for best site performance. I only want it to return logical true when they both satisfy the conditions and return logical true. If you create an array C with the same size as A, the following code works fine: Even though you know that due to the logical indexing only the second to last columns are changed (5x4), the following code does not work. function 'eq' for input arguments of type 'cell'. Learn more about cell arrays, indexing B(isnan(B)) = 0 21: logical(A) Convert numeric values to logical; returns an array that can be used for logical indexing or logical tests. The problem is that the equation that calculates the values in A looks something like this. Edited: James Tursa on 4 Apr 2020 Accepted Answer: James Tursa. L = logical (mod (A,2)) L = 3x3 logical array 1 1 0 1 0 1 0 1 1. You may receive emails, depending on your. correctly governs the placement of the calculated elements. My answer was more intended as a kind of loud thinking, as I was not 100% sure how the assignment works and as my code does need some more complex manipulation. You can index into an array or a table using an array of logical indices. The output of C(B) is, e.g., a 1x10 Array. Use it wherever you can. Both cell arrays are a series of double arrays which match in dimension between the cell arrays, but change size within the cell array. Lead instructor: Mike Fitzpatrick. The syntax is certainly fine since diff_matrix is a logical array. But don't forget it whenever you need to remove or change selected elements in arrays. But these are only two extreme cases. Learn more about cell array;, logical indexing The logical indexing approach should work as you described as wanting it to. Whole array logical indexing: the mask must have the same shape as the array and the returned value is of rank 1 (a vector in Matlab). Pure multidimensional indexing specifies an index variable for each dimension of the array. This is a tutorial on using logical expressions as indexes for vectors and matrices in MATLAB. C and D are also 10x10 arrays. The array C is initalized as a 1x20something Array depending on B. Other MathWorks country sites are not optimized for visits from your location. MathWorks is the leading developer of mathematical computing software for engineers and scientists. Unable to complete the action because of changes made to the page. Just in case someone else is having problems with this, here is some code to explain my former problem and the solution. With your help and insight I am confident I can solve the remaining problems by myself. I guess this does mean that this type of Code does work, even though the right hand side is just composed of vectors, but I do have to watch out which dimensions the vectors have? Accelerating the pace of engineering and science. Thanks for the answer! If you can't tell, I'm not too great at MATLAB, but I am trying. These approaches are indexing by position, linear indexing, and logical indexing. whos logInd "Logical" is one of the builtin types, or classes, of MATLAB matrices. According to the number of dimensions each index variable refers to, indexing can be multidimensional or linear. Reload the page to see its updated state. Cell Arrays and Indexing? In MATLAB®, there are three primary approaches to accessing array elements based on their location (index) in the array. In MATLAB®, there are three primary approaches to accessing array elements based on their location (index) in the array. What i want to achieve is similar to: but i only want to change some values of A, not all of them. Sign in to answer this question. I'm having problems with logical indexing of arrays. Their use comes from MATLAB's logical indexing ability. I did not know that the assignment of elements using a logical array follows the linear index convention, this does clear up some of my confusion. (This is thoroughly discussed in the documentations ection on, If you want to efficiently convert subscripts to linear indices (this is frequently necessary if the subscripts are not continguous), use the, I am not certain exactly what you are doing, however the indexing scheme in my Answer works correctly, and the logical index. This appears to create and replace the correct elements, using the random values my code uses to do the simulation. Other MathWorks country sites are not optimized for visits from your location. Based on your location, we recommend that you select: . You can base this type of indexing on either the values or the positions of elements in the indexing array. Described as wanting it to false otherwise a large logical array and false otherwise a to... 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