[R] with and evaluation
Carl Sutton
suttoncarl at ymail.com
Fri Sep 9 00:57:08 CEST 2016
Hi
I have doing the R-exercises to improve my R programming capabilities. Data.frame exercise 4 showed me that I have a language problem. Here's the problem and my "solution".
# Exercise 4# Create a simple data frame from 3 vectors. Order the entire data frame by the# first column.df2 <- data.frame(a = 5:1,b = letters[1:5], c = runif(5))order(df2$a) Naturally the order function did nothing.
Per "help"Description
order returns a permutation which rearranges its first argument into ascending or descending order, breaking ties by further arguments. sort.list is the same, using only one argument.See the examples for how to use these functions to sort data frames, etc.
Usage
order(..., na.last = TRUE, decreasing = FALSE, method = c("shell", "radix"))
sort.list(x, partial = NULL, na.last = TRUE, decreasing = FALSE, method = c("shell", "quick", "radix"))Arguments
... a sequence of numeric, complex, character or logical vectors, all of the same length, or a classed R object.
Well, doesn't ... mean any legal object? I gave it a legal object and got nada.And the answer absolutely has me screaming "Say What"df2[with(df2,order(a)),]
What's with "with? It is one function I do not use because I find it incomprehensible. To witEvaluate an R expression in an environment constructed from data, possibly modifying (a copy of) the original data.
First of all, if I'm not modifying data (or as a subset activity creating data), why an I doing whatever it is I'm doing? ("possibly modifying (a copy of) the original data.")
Evaluate. According to the thesarus A) assess(v), b) appraise, c) gage.
OK, am I in a safe area? I'll evaluate that. Do I desire future social contact with this person? I'll evaluate that.In no way do I ever evaluate an equation. I may attempt to solve it. I may do a computer program to do the calculations and return a result. I will probably evaluate the result as to whether or not it helps solve the problem. Think in terms of an income tax return. But evaluate an R expression? No clue what that might mean.
The remainder of the definition is also obtuse. an R expression in an environment constructed from data. Why would one make an environment without data? Obviously I am missing the point. My own created function makes a new environment, but I only created it to crunch numbers. If it doesn't crunch numbers it's useless.
The point is, I do not understand the definition of "with" and thus have no idea how to use it. I guess computerese is analogous to taxlawese. Familiar words have entirely different meanings.
Carl Sutton CPA
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