Recently, I wrote a function called copy_names(). It does what you think and a little more: it copies names from one object to another. But it can also attempt to do so even when the sizes of the objects’ dimensions do not match up perfectly. For instance:<\/p>\n
> <\/span>t = matrix(1:9, nrow=3)\r\n<\/span>> <\/span>t2 = t\r\n<\/span>> <\/span>rownames(t) = LETTERS[1:3]; colnames(t) = letters[1:3]\r\n<\/span>> <\/span>t\r\n<\/span> a b c\r\nA 1 4 7\r\nB 2 5 8\r\nC 3 6 9\r\n> <\/span>t2\r\n<\/span> [,1] [,2] [,3]\r\n[1,] 1 4 7\r\n[2,] 2 5 8\r\n[3,] 3 6 9\r\n> <\/span>copy_names(t, t2)\r\n<\/span>> <\/span>t2\r\n<\/span> a b c\r\nA 1 4 7\r\nB 2 5 8\r\nC 3 6 9<\/pre>\nHere we create a matrix and make a copy of it. Then we assign dimension names to the first object. Then we inspect both of them. Unsurprisingly, only the first has names (because R uses copy-on-modify semantics<\/a>). Then we call the copy function and then afterwards we see that the second gets the named copied. Hooray!<\/p>\nWhat if there is imperfect matching? The function will first check whether the number of dimensions is the same and if so, it checks each dimension to see if the lengths match in that dimension. If so, the names are copied. If not, nothing is done. For instance:<\/p>\n
> <\/span>t = matrix(1:6, nrow=3)\r\n<\/span>> <\/span>t2 = matrix(1:9, nrow=3)\r\n<\/span>> <\/span>rownames(t) = LETTERS[1:3]; colnames(t) = letters[1:2]\r\n<\/span>> <\/span>t\r\n<\/span> a b\r\nA 1 4\r\nB 2 5\r\nC 3 6\r\n> <\/span>t2\r\n<\/span> [,1] [,2] [,3]\r\n[1,] 1 4 7\r\n[2,] 2 5 8\r\n[3,] 3 6 9\r\n> <\/span>copy_names(t, t2)\r\n<\/span>> <\/span>t2\r\n<\/span> [,1] [,2] [,3]\r\nA 1 4 7\r\nB 2 5 8\r\nC 3 6 9<\/pre>\nHere we create two matrices, but not of exactly the same sizes: the first is 3×2 and the second is 3×3. Then we assign dimnames to the first. Then we copy to the second and inspect. We see that the only the dimension that matched in length (i.e. the first) had the names copied.<\/p>\n
How does it work?<\/h3>\n
Before I changed it, the code looked like this (including roxygen2 documentation<\/a>):<\/p>\n#' Copy names from one object to another.\r\n#'\r\n#' Attempts to copy names that fit the dimensions of vectors, lists, matrices and data.frames.\r\n#' @param x (an object) An object whose dimnames should be copied.\r\n#' @param y (an object) An object whose dimensions that should be renamed.\r\n#' @keywords names, rownames, colnames, copy\r\n#' @export\r\n#' @examples\r\n#' m = matrix(1:9, nrow=3)\r\n#' n = m\r\n#' rownames(m) = letters[1:3]\r\n#' colnames(m) = LETTERS[1:3]\r\n#' copy_names(m, n)\r\n#' n\r\ncopy_names = function(x, y, partialmatching = T) {\r\n\u00a0 library(stringr)\r\n\u00a0 #find object dimensions\r\n\u00a0 x_dims = get_dims(x)\r\n\u00a0 y_dims = get_dims(y)\r\n\u00a0 same_n_dimensions = length(x_dims) == length(y_dims)\r\n\r\n\u00a0 #what is the object in y parameter?\r\n\u00a0 y_obj_name = deparse(substitute(y))\r\n\r\n\u00a0 #perfect matching\r\n\u00a0 if (!partialmatching) {\r\n\u00a0\u00a0\u00a0 #set names if matching dims\r\n\u00a0\u00a0\u00a0 if (all(x_dims == y_dims)) {\r\n\u00a0\u00a0\u00a0\u00a0\u00a0 attr(y, \"dimnames\") = attr(x, \"dimnames\")\r\n\u00a0\u00a0\u00a0 } else {\r\n\u00a0\u00a0\u00a0\u00a0\u00a0 stop(str_c(\"Dimensions did not match! \", x_dims, \" vs. \", y_dims))\r\n\u00a0\u00a0\u00a0 }\r\n\u00a0 }\r\n\r\n\u00a0 #if using partial matching and dimensions match in number\r\n\u00a0 if (same_n_dimensions && partialmatching) {\r\n\u00a0\u00a0\u00a0 #loop over each dimension\r\n\u00a0\u00a0\u00a0 for (dim in 1:length(dimnames(x))) {\r\n\u00a0\u00a0\u00a0\u00a0\u00a0 #do lengths match?\r\n\u00a0\u00a0\u00a0\u00a0\u00a0 if (x_dims[dim] == y_dims[dim]) {\r\n\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 dimnames(y)[[dim]] = dimnames(x)[[dim]]\r\n\u00a0\u00a0\u00a0\u00a0\u00a0 }\r\n\u00a0\u00a0\u00a0 }\r\n\u00a0 }\r\n\r\n\u00a0 #assign in the outer envir\r\n\u00a0 assign(y_obj_name, value = y, pos = 1)\r\n}<\/pre>\n