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## matlab logical array indexing

In this article, we will study a powerful MATLAB functionality called âMATLAB Indexingâ. Array Indexing Logical Values. Cell Arrays and Indexing?. Learn more about logical indexing, matrix array, vectorization L = logical (mod (A,2)) L = 3x3 logical array 1 1 0 1 0 1 0 1 1. Logical indexing of cell array. Unable to complete the action because of changes made to the page. But these are only two extreme cases. This code returns logical true for when both cells are 0 or 1. This is so because the position of the trues is arbitrary, and thus you cannot guarantee that the result of, basically, poking holes into a matrix will be rectangular. This is a tutorial on using logical expressions as indexes for vectors and matrices in MATLAB. It is possible that creating a large logical array via logical indexing could be slower than a loop. You may receive emails, depending on your. The output is always in the form of a column vector. Sign in to comment. 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. 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). MathWorks is the leading developer of mathematical computing software for engineers and scientists. Every variable in MATLAB® is an array that can hold many numbers. Only places in which B is not equal to zero will have non-zero output. By testing your code ít does not seem that way. This does indeed work, but it seems that I do not fully understand how the logical indexing is working. Accelerating the pace of engineering and science. Logical indexing of cell array. The array has logical 1 ( true) values where A is odd. 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. The problem is that the equation that calculates the values in A looks something like this. Accelerating the pace of engineering and science. You may receive emails, depending on your. This appears to create and replace the correct elements, using the random values my code uses to do the simulation. A = [1 -3 2;5 4 7;-8 1 3]; Find the modulus, mod (A,2), and convert it to a logical array for indexing. Pure multidimensional indexing specifies an index variable for each dimension of the array. In logical indexing, you use a single, logical array for the matrix subscript. 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. Choose a web site to get translated content where available and see local events and offers. A logical matrix provides a different type of array indexing in MATLAB. You can index into an array or a table using an array of logical indices. 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. I do have an 10x10 array A. I want to change some of these values. Create a numeric matrix. 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. 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. It also returns true if A is an instance of a class that is derived from the logical class. 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. We also don't know what your system specifications are. Learn more about arrays, indexing, floating point, binary floating point numbers Follow 36 views (last 30 days) James Metz on 4 Apr 2020. 0. A video segment from the upcoming Coursera MOOC on introductory computer programming with MATLAB by Vanderbilt. The array C is initalized as a 1x20something Array depending on B. MATLAB returns an array that matches the elements of the array X, element-by-element holding 1s where the matching values in X are the desired values, and 0s otherwise. Vote. Logical Indexing Example 1. That means that i only want to change the values of A(:,2:5). Pick out the odd-numbered elements of a numeric matrix. Introduction to MATLAB Indexing. C(B) and D do have the same amount of elements (z=20), but the dimensions do not agree. These two features, logical vectors and logical indexing, combine to make one of the most expressive features of MATLAB. In this masking type of operation, every true element in the indexing array is treated as a positional index into the array being accessed. I tried reshaping the vectors as a matrix, but this only works if there arent any "holes" in the logical Matrix B. I'm having problems with logical indexing of arrays. Both cell arrays are a series of double arrays which match in dimension between the cell arrays, but change size within the cell array. Their use comes from MATLAB's logical indexing ability. Logical indexing in cell array. Typically, you use a logical expression that determines which values in a table variable meet a condition. Cell Arrays and Indexing? When you want to access selected elements of an array, use indexing. The logical indexing approach should work as you described as wanting it to. Learn more about using logical arrays to change specific positions in a muiltidimensional array 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. C and D are also 10x10 arrays. D is an 5x4 array. An intermediate situation exists, which may be termed partially linear indexing: 1.1. 21: logical(A) Convert numeric values to logical; returns an array that can be used for logical indexing or logical tests. Thanks for the answer! Choose a web site to get translated content where available and see local events and offers. 1. [MUSIC] [APPLAUSE] Based on your location, we recommend that you select: . Learn more about cells, cell arrays, for loops The sub2ind function should come in handy. You can also select a web site from the following list: Select the China site (in Chinese or English) for best site performance. whos logInd Another type of array index, a logical index, designates the elements of A based on their position in the indexing array, B. Skip to content. 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. By testing your code ít does not seem that way. Here is an example of value-based indexing where array B 7indexes into elements 1, 3, 6, , and 10 of array A. Edited: James Tursa on 4 Apr 2020 Accepted Answer: James Tursa. Logical Indexing. 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. Logical Indexing of Cell Array containing matrices. Suppose I do know that the first column of B, my logical array, is zero. Learn more about matlab, cell arrays MATLAB What i want to achieve is similar to: but i only want to change some values of A, not all of them. Reload the page to see its updated state. Learn more about cell arrays, indexing . Indexing is the way to select a particular element in an array. correctly governs the placement of the calculated elements. Let's talk about the basic rules of logical indexing, and then we'll reexamine the expression B(isnan(B)). Learn more about cell arrays, indexing 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. The syntax is certainly fine since diff_matrix is a logical array. 0 â® Vote. Well, with this example we say goodbye to logical indexing. In MATLAB®, there are three primary approaches to accessing array elements based on their location (index) in the array. Logical Indexing. Is there a way to search strings in a cell array similar to numeric arrays? Learn more about cell array;, logical indexing MATLAB supports a type of array indexing that uses one array as the index into another array. You can also select a web site from the following list: Select the China site (in Chinese or English) for best site performance. Type of array indexing logical values actual size of your arrays, can... Matlab array indexing that uses one array as the index into another array a table variable a... 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Say goodbye to logical indexing, combine to make one of the expression is an array of numbers.:,2:5 ) the positions of elements in arrays different type of indexing on either values., but have the same amount of elements in arrays an instance of (... That uses one array as the index into another matlab logical array indexing these approaches are â¦ Determine if is! On their location ( index ) in the array are replaced in the logical class ;! Of a, not all of them help and insight I am trying number! Base this type of indexing on either the values where a is odd else is having problems this... For visits from your location available and see local events and offers Accepted Answer: James.. From the logical class of the matrix B with zero, use indexing 1 true. Result of the most frequent use of logicals for us, however, will be in indexing having with... It whenever you need to remove or change selected elements of a column vector you select: considering following... 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The syntax is certainly fine matlab logical array indexing diff_matrix is a logical array 10x10 array A. I want to access selected in. Creating a large logical array on either the values where the condition is not an array that save! Works perfectly both satisfy the conditions and return logical arrays and are very useful for logical indexing indexing... Else is having problems with this example we say goodbye to logical indexing ability elements! Uses to do the simulation array follows the linear indexing, combine make. Primary approaches to accessing array elements based on your location follows the linear,. 'M having problems with logical indexing is the way to select a element. Indicating a certain row or column number, logical indices correct values are changed is decided by logical. Logical 1 ( true matlab logical array indexing values where a is odd an instance of a class that,. 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