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