5 1 2 # First element of the first column dimnames(B) ]Īccessing matrix elements is similar to access dataframes in R. If you only want to return your column and row names you can use the dimnames function instead and access the elements of the list to get the row names or the column names. Moreover, with the attributes function you can access the dimension and the column and row labels of your matrices. Note that you could rename the matrix columns and rows the same way. Rownames(B) <- paste0("Row ", 1:nrow(B)) # EquivalentĬolnames(B) <- c("Column 1", "Column 2", "Column 3")Ĭolnames(B) <- paste0("Column ", 1:ncol(B)) # Equivalent You can assign names to the rows and columns of a matrix with the rownames and colnames functions. my_matrix <- matrix(1:12, ncol = 2, byrow = FALSE) Matrix(c("red", "green", "orange", "black"), ncol = 2) Īlso, you can know the dimensions of your matrix in R programming with the dim function. matrix(c(TRUE, TRUE, FALSE, TRUE), ncol = 2) Note you can use any data type inside a matrix, as long as they are homogeneous. Typeof(cbind(x, y)) # "double" # By columns # By rows Note that the output class can be checked with the class function and the class of the elements with the typeof function. If you have data stored in vectors or in the columns of a data frame, you can use the cbind for column binding or rbind for row binding and the output will be of class matrix. Matrix(data, ncol = 2, byrow = TRUE) # By columns # By rows Matrix(data, ncol = 2, nrow = 3) # Equivalent ![]() Matrix(data, ncol = 2, byrow = FALSE) # byrow = FALSE by default By default, the function will order the input by columns. Also, you can specify if the matrix is ordered by rows or by columns with the byrow argument. However, you can set the number of columns or the number of rows with the ncol and nrow arguments, respectively. data <- 1:6Īs you can observe in the output the function will create by default a matrix of one column and as many rows as the length of the vector. The matrix function allows creating a matrix data structure in R programming language, passing a numeric, character or logical vector. 3 Remove NA, NaN and Inf values from matrix.1.1 Add and delete column to matrix in R.But you can get the pointer to the array and since a pointer is an iterator, you can pass it into an algorithm. ( *) update: unique_ptr is not a container, so it won’t work with standard algorithms… at least out of the box. Is not a container, so it doesn’t work with standard algorithms( *) ![]() Has no pointers, iterators, so you can only invalidate it by swapĬompatibility with concepts and algorithms Vector may invalidate pointers and iterators when you have a reallocation O(n) time swap and move operations, where n is the number of elements in the arrayĮnsures pointers, references and iterators will never be invalidated while the object is live, even on swap() And some people get their arrays from other code that is known to return an array and that code isn’t going to be rewritten to return a vector or something.Īnd here’s a nice comparison for each technique: Use caseĭoes not allow resizing (unless you recreate the whole thing) Some people need a dynamically sized array, so std::array is out. Some people do not have the luxury of using std::vector, even with allocators. I got several interesting answers, and we can summarize them with the following quote: When I wrote my early blog post on smart pointers - C++ Smart Pointers Gotchas - C++ Stories, back in 2013, I also asked a question at Stack Overflow.Ĭ++ - Is there any use for unique_ptr with array? - Stack OverflowĪnd so far, it’s one of my most voted questions :) Let’s have a look at some possible use cases. I guess it’s much more convenient to use std::vector and pass it around than passing unique_ptr? Ok, we covered how to create pointers and even saw some recent updates in C++20… but should we even use it? The _for_overwrite functions allow for even 20x init speed up of the initialization code! See my premium article with a benchmark which is available for C++ Stories Premium/Patreon members.
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