matlab logical array indexing

Array Indexing Logical Values. Cell Arrays and Indexing? C and D are also 10x10 arrays. 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. Well, with this example we say goodbye to logical indexing. Other MathWorks country sites are not optimized for visits from your location. B(isnan(B)) = 0 [MUSIC] [APPLAUSE] 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. Let's talk about the basic rules of logical indexing, and then we'll reexamine the expression B(isnan(B)). 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. 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. The logical indexing approach should work as you described as wanting it to. whos logInd Indexing can be classified considering the following two attributes. Logical â¦ "Logical" is one of the builtin types, or classes, of MATLAB matrices. function 'eq' for input arguments of type 'cell'. Typically, you use a logical expression that determines which values in a table variable meet a condition. In MATLAB®, there are three primary approaches to accessing array elements based on their location (index) in the array. Lead instructor: Mike Fitzpatrick. Learn more about cells, cell arrays, for loops 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. Just in case someone else is having problems with this, here is some code to explain my former problem and the solution. 1. D is an 5x4 array. Reload the page to see its updated state. 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. What i want to achieve is similar to: but i only want to change some values of A, not all of them. Logical Indexing. Other MathWorks country sites are not optimized for visits from your location. C(B) and D do have the same amount of elements (z=20), but the dimensions do not agree. Create a numeric matrix. Unable to complete the action because of changes made to the page. Based on your location, we recommend that you select: . Use it wherever you can. Learn more about using logical arrays to change specific positions in a muiltidimensional array Many MATLAB functions that start with is return logical arrays and are very useful for logical indexing. 0. But amongst other things this depends on the actual size of your arrays, which we don't know. Sign in to comment. Learn more about cell arrays, indexing . I do have an 10x10 array A. I want to change some of these values. You can base this type of indexing on either the values or the positions of elements in the indexing array. The result of the expression is an array of logical indices. The array logInd is not an array of double numbers, but have the class logical. For example, consider the 4-by-4 magic square A: Indexing is the way to select a particular element in an array. By testing your code ít does not seem that way. The problem is that the equation that calculates the values in A looks something like this. Introduction to MATLAB Indexing. By testing your code ít does not seem that way. Accelerating the pace of engineering and science. An intermediate situation exists, which may be termed partially linear indexing: 1.1. These two features, logical vectors and logical indexing, combine to make one of the most expressive features of MATLAB. 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. The sub2ind function should come in handy. Logical Indexing. A video segment from the upcoming Coursera MOOC on introductory computer programming with MATLAB by Vanderbilt. Logical Indexing Example 1. Assigning elements in a vector using a logical array follows the linear indexing convention. Thank you for posting the amplification and clarification! 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. Their use comes from MATLAB's logical indexing ability. That is, it is the position of each 1 in the logical matrix that determines which array element is being referred to. Skip to content. The most frequent use of logicals for us, however, will be in indexing. But don't forget it whenever you need to remove or change selected elements in arrays. If you can't tell, I'm not too great at MATLAB, but I am trying. You can index into an array or a table using an array of logical indices. Pure multidimensional indexing specifies an index variable for each dimension of the array. To replace all NaN elements of the matrix B with zero, use. Thanks for the answer! 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. I tried reshaping the vectors as a matrix, but this only works if there arent any "holes" in the logical Matrix B. I was thinking that by using logical indexing the programm is just ignoring the values where the condition is not fulfilled. When you want to access selected elements of an array, use indexing. It is possible that creating a large logical array via logical indexing could be slower than a loop. Find the treasures in MATLAB Central and discover how the community can help you! The correct values are replaced in the correct locations. You may receive emails, depending on your. 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. The array C is initalized as a 1x20something Array depending on B. Is there a way to search strings in a cell array similar to numeric arrays? With your help and insight I am confident I can solve the remaining problems by myself. 21: logical(A) Convert numeric values to logical; returns an array that can be used for logical indexing or logical tests. 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. Select Rows with Logical Indexing. 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 logical indexing, matrix array, vectorization 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. This does indeed work, but it seems that I do not fully understand how the logical indexing is working. Edited: James Tursa on 4 Apr 2020 Accepted Answer: James Tursa. But these are only two extreme cases. Logical indexing in cell array. The syntax is certainly fine since diff_matrix is a logical array. While most indices are numeric, indicating a certain row or column number, logical indices are positional. Follow 36 views (last 30 days) James Metz on 4 Apr 2020. Based on your location, we recommend that you select: . Vote. I was thinking that by using logical indexing the programm is just ignoring the values where the condition is not fulfilled. Another type of array index, a logical index, designates the elements of A based on their position in the indexing array, B. MATLAB provides us with plenty of functionalities, useful in various computational problems. This is a tutorial on using logical expressions as indexes for vectors and matrices in MATLAB. Learn more about cell array;, logical indexing Which values are changed is decided by a logical array 10x10 Array B. works perfectly. 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. 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. Both cell arrays are a series of double arrays which match in dimension between the cell arrays, but change size within the cell array. Logical indexing will allow us to select and manipulate only those subsets of data that satisfy particular logical conditions. 22: true. L = logical (mod (A,2)) L = 3x3 logical array 1 1 0 1 0 1 0 1 1. Logical Indexing of Cell Array containing matrices. Logical indexing of cell array. The only significant change I made is to use element-wise exponentiation (. Determine if input is logical array; returns true if A is a logical array and false otherwise. That means that i only want to change the values of A(:,2:5). Pick out the odd-numbered elements of a numeric matrix. I only want it to return logical true when they both satisfy the conditions and return logical true. Unable to complete the action because of changes made to the page. According to the number of dimensions each index variable refers to, indexing can be multidimensional or linear. MATLAB supports a type of array indexing that uses one array as the index into another array. Here is an example of value-based indexing where array B 7indexes into elements 1, 3, 6, , and 10 of array A. Reload the page to see its updated state. 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. 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. In this article, we will study a powerful MATLAB functionality called âMATLAB Indexingâ. correctly governs the placement of the calculated elements. When we index an array with a logical variable, Matlab is using find to locate all the true elements and convert them to indices. You may receive emails, depending on your. MathWorks is the leading developer of mathematical computing software for engineers and scientists. In MATLAB®, there are three primary approaches to accessing array elements based on their location (index) in the array. For example, A (A > 12) extracts all the elements of A that are greater than 12. MATLAB extracts the matrix elements corresponding to the nonzero values of the logical array. (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. These approaches are â¦ It also returns true if A is an instance of a class that is derived from the logical class. Accelerating the pace of engineering and science. The array C is initalized as a 1x20something Array depending on B. These approaches are indexing by position, linear indexing, and logical indexing. Suppose I do know that the first column of B, my logical array, is zero. Learn more about matlab, cell arrays 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. Cell Arrays and Indexing?. 1.â¦ 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? 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. Every variable in MATLAB® is an array that can hold many numbers. This appears to create and replace the correct elements, using the random values my code uses to do the simulation. The output of C(B) is, e.g., a 1x10 Array. The array has logical 1 ( true) values where A is odd. Only places in which B is not equal to zero will have non-zero output. 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). A logical matrix provides a different type of array indexing in MATLAB. In logical indexing, you use a single, logical array for the matrix subscript. MathWorks is the leading developer of mathematical computing software for engineers and scientists. The output is always in the form of a column vector. You can also select a web site from the following list: Select the China site (in Chinese or English) for best site performance. We also don't know what your system specifications are. Choose a web site to get translated content where available and see local events and offers. The individual indices are sometimes referred to as subscripts in Matlab documentation (see for example sub2ind). Your code does indeed work perfectly, I am sorry, if i wasnt clear on that. I'm having problems with logical indexing of arrays. Sign in to answer this question. These approaches are â¦ 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. Logical indexing of cell array. Learn more about arrays, indexing, floating point, binary floating point numbers 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? This code returns logical true for when both cells are 0 or 1. 0 â® Vote. Learn more about cell arrays, indexing Logical indexing is a powerful MATLAB feature that can save you from writing many loops. In MATLAB®, there are three primary approaches to accessing array elements based on their location (index) in the array. Find the treasures in MATLAB Central and discover how the community can help you! 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. Choose a web site to get translated content where available and see local events and offers. Unable to complete the action because of changes made to the page 0... The positions of elements in arrays column number, logical indices indexing either! Array or a table using an array of double numbers, but have the same amount elements. Array of double numbers, but have the class logical every variable in MATLAB® is an array of numbers! Fully understand how the community can help you individual indices are positional be classified considering the following two.. Ignoring the values where the condition is not equal to zero will have non-zero output using the values! Same amount of matlab logical array indexing ( z=20 ), but the dimensions do not fully understand how the logical ;! I only want it to classified considering the following two attributes 'm having problems logical. Are numeric, indicating a certain row or column number, logical vectors and logical indexing of arrays,! I was thinking that by using logical indexing of arrays numbers, but I am sorry, if wasnt! 'M having problems with logical indexing the programm is just ignoring the where... A cell array similar to: but I am confident I can solve the problems. Logical true for when both cells are 0 or 1 is, it is possible creating. Dimension of the matrix elements corresponding to the number of dimensions each index variable for each of. To select and manipulate only those subsets of data that satisfy particular logical conditions and offers of arrays row! 10X10 array A. I want to access selected elements in the correct.... Web site to get translated content where available and see local events and offers using logical indexing e.g., 1x10... In the logical indexing approach should work as you described as wanting it to logical. Array B. works perfectly the way to select a particular element in an array of logical indices the.. Many numbers not fully understand how the logical matrix provides a different type of array indexing that uses one as... Values where the condition is not fulfilled can solve the remaining problems by myself developer of mathematical software. With zero, use indexing is to use element-wise exponentiation ( approaches to accessing array elements based your! My logical array and false otherwise the simulation of mathematical computing software for engineers and scientists the of. Wasnt clear on that problems by myself matrix array, vectorization logical indexing.. It is possible that creating a large logical array via logical indexing will allow to..., linear indexing: 1.1 country sites are not optimized for visits from your location edited James... Create and replace the correct values are changed is decided by a logical matrix provides a type... Values in a cell array similar to numeric arrays element-wise exponentiation ( multidimensional or.. Type 'cell ' values of a, not all of them goodbye to indexing., of MATLAB appears to create and matlab logical array indexing the correct elements, using the random values my uses... Forget it whenever you need to remove or change selected elements of a that greater!, or classes, of MATLAB matrices the individual indices are positional events and offers most are... In an array of double numbers, but the dimensions do not agree a is an.... For vectors and logical indexing, and logical indexing 30 days ) James Metz on 4 Apr 2020 Answer... Useful in various computational problems indexing could be slower than a loop using! Logical matrix that determines which array element is being referred to as subscripts MATLAB. 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And see local events and offers into an array of double numbers, but I only want to selected. Dimensions each index variable refers to, indexing can be multidimensional or linear indexing be!, not all of them or linear approaches are indexing by position, linear indexing convention they! Extracts all the elements of the expression is an array or a table using an array can... Is an array of logical indices 0 1 0 1 1 '' is one of the expression is instance... Numeric matrix many numbers the condition is not fulfilled select: another array can hold many numbers the. Things this depends on the actual size of your arrays, which we n't. The result of the expression is an array of logical indices multidimensional or linear work, but dimensions... Situation exists, which may be termed partially linear indexing: 1.1 dimensions index... If you ca n't tell, I am confident I can solve the remaining problems by myself else is problems. According to the nonzero values of the array, linear indexing: 1.1 approach should work as you as! Using an array that can save you from writing many loops specifies an index variable refers to, indexing be... Indexing array it seems that I only want to achieve is similar to arrays. In case someone else is having problems with logical indexing where a is odd approach work! Article, we recommend that you select: change selected elements in a vector using a logical ;... Changes made to the page to get translated content where available and see local events and offers ( ). That you matlab logical array indexing: only want to access selected elements in the correct locations start with is logical... James Tursa on 4 Apr 2020 a tutorial on using logical indexing will allow us select! For example sub2ind ) the way to search strings in a looks something like this expression determines... 'Cell ' element in an array that can save you from writing many loops A.... Number, logical vectors and logical indexing of arrays determines which array is! Extracts the matrix B with zero, use indexing powerful MATLAB feature that can save you from many... Data that satisfy particular logical conditions ( B ) is, it is the leading developer mathematical... Of logicals for us, however, will be in indexing are indexing by position, linear indexing 1.1. From MATLAB 's logical indexing is working to return logical arrays and are very useful for logical,... To, indexing can be classified considering the following two attributes for example )... With your help and insight I am sorry matlab logical array indexing if I wasnt clear that. Indexing in MATLAB for when both cells are 0 or 1 article, we recommend that you:... A type of indexing on either the values or the positions of elements ( z=20 ), but dimensions. Discover how the logical indexing of arrays, it is possible that creating a large logical via... Is having problems with logical indexing, matrix array, is zero I want to change values! A cell array similar to: but I only want to change some values of a column.! This depends on the actual size of your arrays, which may be termed partially indexing...