R simply returns the last object evaluated. This is how R displays the result.Ī note for the following: in most cases, R can return a value even if the latter has not been specified, or more precisely the return value of the function has not been assigned to a variable. The output of the above code, a line vector, would have also been given if you summed along the lines of the matrix. You end up with a line vector containing the sums of the values of each column. Note that, to avoid cluttering the picture, just one of the columns is highlighted. That means that the instruction you have just entered, depicted in figure 1, translates into: “apply the function ‘sum’ to the matrix X along margin 2 (by column), summing up the values of each column. Remember that in R, a matrix can be seen as a collection of line vectors when you cross the matrix from top to bottom (along the vertical line 1, which specifies the dimension or margin 1), or as a list of columns vectors, spanning the matrix left to right along the dimension or margin 2. Well, this depends on the structure of the data that you want to operate on and the format of the output that you need.Į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 More specifically, the family is made up of the apply(), lapply(), sapply(), vapply(), mapply(), rapply(), and tapply() functions. The apply() functions form the basis of more complex combinations and helps to perform operations with very few lines of code. Other vectorized functions, which yield more complex structures like lists, vectors, matrices, and arrays.
They act on an input list, matrix or array and apply a named function with one or several optional arguments. These functions allow crossing the data in a number of ways and avoid explicit use of loop constructs. The apply() family pertains to the R base package and is populated with functions to manipulate slices of data from matrices, arrays, lists and dataframes in a repetitive way.
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