non-standard-evaluation

I was attempting to answer this nice question about creating a non-standard evaluating function for a data.table object, doing a grouped sum. Akrun came up with a lovely answer which I'll simplify here: akrun <- function(data, var, group){ var <- substitute(var) group <- substitute(group) data[, sum(eval(var)), by = group] } library(data.table) mt = as.data.table(mtcars) akrun(mt, cyl, mpg) # group V1 # 1: 6 138.2 # 2: 4 293.3 # 3: 8 211.4 I was also working on an answer, and had close to the same answer, but with the substitute s inline with the rest. Mine results in an error: gregor =

For an arbitrary function f <- function(x, y = 3){ z <- x + y z^2 } I want to be able take the argument names of f > argument_names(f) [1] "x" "y" Is this possible? formalArgs and formals are two functions that would be useful in this case. If you just want the parameter names then formalArgs will be more useful as it just gives the names and ignores any defaults. formals gives a list as the output and provides the parameter name as the name of the element in the list and the default as the value of the element. f <- function(x, y = 3){ z <- x + y z^2 } > formalArgs(f) [1] "x" "y" > formals(f)

This question already has an answer here: Reshaping multiple sets of measurement columns (wide format) into single columns (long format) 7 answers I am trying to write a function that will convert this data frame library(dplyr) library(rlang) library(purrr) df <- data.frame(obj=c(1,1,2,2,3,3,3,4,4,4), S1=rep(c("a","b"),length.out=10),PR1=rep(c(3,7),length.out=10), S2=rep(c("c","d"),length.out=10),PR2=rep(c(7,3),length.out=10)) obj S1 PR1 S2 PR2 1 1 a 3 c 7 2 1 b 7 d 3 3 2 a 3 c 7 4 2 b 7 d 3 5 3 a 3 c 7 6 3 b 7 d 3 7 3 a 3 c 7 8 4 b 7 d 3 9 4 a 3 c 7 10 4 b 7 d 3 In to this data frame df %>%

I am trying to search a database and then label the ouput with a name derived from the original search, "derived_name" in the reproducible example below. I am using a dplyr pipe %>% , and I am having trouble with quasiquotation and/or non-standard evaluation. Specifically, using count_colname , a character object derived from "derived_name" , in the final top_n() function fails to subset the dataframe. search_name <- "derived_name" set.seed(1) letrs <- letters[rnorm(52, 13.5, 5)] letrs_count.df <- letrs %>% table() %>% as.data.frame() count_colname <- paste0(search_name, "_letr_count")

Consider this use of ggplot(...) inside a function. x <- seq(1,10,by=0.1) df <- data.frame(x,y1=x, y2=cos(2*x)/(1+x)) library(ggplot2) gg.fun <- function(){ i=2 plot(ggplot(df,aes(x=x,y=df[,i]))+geom_line()) } if(exists("i")) remove(i) gg.fun() # Error in `[.data.frame`(df, , i) : object 'i' not found i=3 gg.fun() # plots df[,3] vs. x It looks like ggplot does not recognize the variable i defined inside the function, but does recognize i if it is defined in the global environment. Why is that? Note that this gives the expected result. gg.new <- function(){ i=2 plot(ggplot(data.frame(x=df$x,y