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. MATLAB supports a type of array indexing that uses one array as the index into another array. C(B) and D do have the same amount of elements (z=20), but the dimensions do not agree. You may receive emails, depending on your. 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. MathWorks is the leading developer of mathematical computing software for engineers and scientists. Choose a web site to get translated content where available and see local events and offers. In MATLAB®, there are three primary approaches to accessing array elements based on their location (index) in the array. The syntax is certainly fine since diff_matrix is a logical array. Logical Indexing. It also returns true if A is an instance of a class that is derived from the logical class. With your help and insight I am confident I can solve the remaining problems by myself. While most indices are numeric, indicating a certain row or column number, logical indices are positional. Learn more about arrays, indexing, floating point, binary floating point numbers Create a numeric matrix. I was thinking that by using logical indexing the programm is just ignoring the values where the condition is not fulfilled. This is a tutorial on using logical expressions as indexes for vectors and matrices in MATLAB. Learn more about matlab, cell arrays MATLAB 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 cell arrays, indexing The logical indexing approach should work as you described as wanting it to. 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. A video segment from the upcoming Coursera MOOC on introductory computer programming with MATLAB by Vanderbilt. For example, one random assignment produces: 0.19812 0.052677 0.94274 0.66634 0.12801, 0.48969 0.73786 0.41774 0.53913 0.99908, 0.33949 0.26912 0.98305 0.69811 0.17112, 0.95163 0.42284 0.30145 0.66653 0.032601, 0.92033 0.54787 0.7011 0.17813 0.5612, 10048 1898 0.94274 0.66634 2173, 4633 0.73786 881 0.53913 0.99908, 3842 3637 0.98305 0.69811 7085, 0.95163 12968 8066 0.66653 11453, 0.92033 0.54787 0.7011 7940 0.5612. When you want to access selected elements of an array, use indexing. This does indeed work, but it seems that I do not fully understand how the logical indexing is working. Pick out the odd-numbered elements of a numeric matrix. 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. For example, consider the 4-by-4 magic square A: The correct values are replaced in the correct locations. 22: true. function 'eq' for input arguments of type 'cell'. You can base this type of indexing on either the values or the positions of elements in the indexing array. Logical indexing will allow us to select and manipulate only those subsets of data that satisfy particular logical conditions. Select Rows with Logical Indexing. Sign in to comment. These approaches are â¦ Logical â¦ We also don't know what your system specifications are. Based on your location, we recommend that you select: . Logical Indexing of Cell Array containing matrices. If i want to make the following code work, i guess i do have to transpose the 5x4 Array E into a vector with the same length as C(B) and D(B), am I right? The problem is that the equation that calculates the values in A looks something like this. I do have an 10x10 array A. I want to change some of these values. The output is always in the form of a column vector. Use it wherever you can. Accelerating the pace of engineering and science. The array C is initalized as a 1x20something Array depending on B. Vote. Well, with this example we say goodbye to logical indexing. whos logInd Determine if input is logical array; returns true if A is a logical array and false otherwise. MATLAB provides us with plenty of functionalities, useful in various computational problems. According to the number of dimensions each index variable refers to, indexing can be multidimensional or linear. In this article, we will study a powerful MATLAB functionality called âMATLAB Indexingâ. It is possible that creating a large logical array via logical indexing could be slower than a loop. Other MathWorks country sites are not optimized for visits from your location. In MATLAB®, there are three primary approaches to accessing array elements based on their location (index) in the array. Is there a way to search strings in a cell array similar to numeric arrays? Thank you for posting the amplification and clarification! Reload the page to see its updated state. [MUSIC] [APPLAUSE] Which values are changed is decided by a logical array 10x10 Array B. works perfectly. Other MathWorks country sites are not optimized for visits from your location. 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). Indexing can be classified considering the following two attributes. 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. That means that i only want to change the values of A(:,2:5). That is, it is the position of each 1 in the logical matrix that determines which array element is being referred to. Lead instructor: Mike Fitzpatrick. 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 logical indexing, matrix array, vectorization L = logical (mod (A,2)) L = 3x3 logical array 1 1 0 1 0 1 0 1 1. MathWorks is the leading developer of mathematical computing software for engineers and scientists. Sign in to answer this question. Logical indexing of cell array. Your code does indeed work perfectly, I am sorry, if i wasnt clear on that. 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. Follow 36 views (last 30 days) James Metz on 4 Apr 2020. Assigning elements in a vector using a logical array follows the linear indexing convention. Reload the page to see its updated state. Edited: James Tursa on 4 Apr 2020 Accepted Answer: James Tursa. Accelerating the pace of engineering and science. Logical Indexing Example 1. What i want to achieve is similar to: but i only want to change some values of A, not all of them. You can index into an array or a table using an array of logical indices. 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. Suppose I do know that the first column of B, my logical array, is zero. 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. 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 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. 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. I was thinking that by using logical indexing the programm is just ignoring the values where the condition is not fulfilled. Choose a web site to get translated content where available and see local events and offers. 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. Let's talk about the basic rules of logical indexing, and then we'll reexamine the expression B(isnan(B)). Their use comes from MATLAB's logical indexing ability. I only want it to return logical true when they both satisfy the conditions and return logical true. The array has logical 1 ( true) values where A is odd. Unable to complete the action because of changes made to the page. 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. This code returns logical true for when both cells are 0 or 1. The result of the expression is an array of logical indices. 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. 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. Here is an example of value-based indexing where array B 7indexes into elements 1, 3, 6, , and 10 of array A. Both cell arrays are a series of double arrays which match in dimension between the cell arrays, but change size within the cell array. Unable to complete the action because of changes made to the page. MATLAB extracts the matrix elements corresponding to the nonzero values of the logical array. The output of C(B) is, e.g., a 1x10 Array. You can also select a web site from the following list: Select the China site (in Chinese or English) for best site performance. But amongst other things this depends on the actual size of your arrays, which we don't know. But don't forget it whenever you need to remove or change selected elements in arrays. Cell Arrays and Indexing? Find the treasures in MATLAB Central and discover how the community can help you! If you can't tell, I'm not too great at MATLAB, but I am trying. For example, A (A > 12) extracts all the elements of A that are greater than 12. 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? Learn more about cell arrays, indexing . "Logical" is one of the builtin types, or classes, of MATLAB matrices. The sub2ind function should come in handy. 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. The array C is initalized as a 1x20something Array depending on B. Skip to content. D is an 5x4 array. 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. But these are only two extreme cases. I'm having problems with logical indexing of arrays. In MATLAB®, there are three primary approaches to accessing array elements based on their location (index) in the array. By testing your code ít does not seem that way. This appears to create and replace the correct elements, using the random values my code uses to do the simulation. Introduction to MATLAB Indexing. A logical matrix provides a different type of array indexing in MATLAB. These two features, logical vectors and logical indexing, combine to make one of the most expressive features of MATLAB. 1. Learn more about cells, cell arrays, for loops Logical indexing of cell array. In logical indexing, you use a single, logical array for the matrix subscript. To replace all NaN elements of the matrix B with zero, use. 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. Learn more about cell array;, logical indexing Array Indexing Logical Values. 21: logical(A) Convert numeric values to logical; returns an array that can be used for logical indexing or logical tests. Logical indexing is a powerful MATLAB feature that can save you from writing many loops. Find the treasures in MATLAB Central and discover how the community can help you! B(isnan(B)) = 0 The only significant change I made is to use element-wise exponentiation (. These approaches are â¦ (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. 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. Typically, you use a logical expression that determines which values in a table variable meet a condition. Cell Arrays and 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. 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. Pure multidimensional indexing specifies an index variable for each dimension of the array. Logical Indexing. I tried reshaping the vectors as a matrix, but this only works if there arent any "holes" in the logical Matrix B. Logical indexing in cell array. 0. The individual indices are sometimes referred to as subscripts in Matlab documentation (see for example sub2ind). Many MATLAB functions that start with is return logical arrays and are very useful for logical indexing. You may receive emails, depending on your. Just in case someone else is having problems with this, here is some code to explain my former problem and the solution. By testing your code ít does not seem that way. Thanks for the answer! C and D are also 10x10 arrays. Based on your location, we recommend that you select: . 0 â® Vote. 1.â¦ The array logInd is not an array of double numbers, but have the class logical. These approaches are indexing by position, linear indexing, and logical indexing. Learn more about using logical arrays to change specific positions in a muiltidimensional array Another type of array index, a logical index, designates the elements of A based on their position in the indexing array, B. The most frequent use of logicals for us, however, will be in indexing. correctly governs the placement of the calculated elements. Does not seem that way of mathematical computing software for engineers and scientists appears to create and the. Are replaced in the array has logical 1 ( true ) values where condition... 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Your arrays, indexing logical values most frequent use of logicals for us, however, will in., combine to make one of the builtin types, or classes, of MATLAB an. Individual indices are positional ) is, it is the position of each 1 the... ), but have the class logical expression is an array of logical indices are,! Are replaced in the form of a, not all of them that...