non-standard-evaluation

问题 Somewhat hard to define this question without sounding like lots of similar questions! I have a function for which I want one of the parameters to be a function name, that will be passed to dplyr::summarise, e.g. "mean" or "sum": data(mtcars) f <- function(x = mtcars, groupcol = "cyl", zCol = "disp", zFun = "mean") { zColquo = quo_name(zCol) cellSummaries <- x %>% group_by(gear, !!sym(groupcol)) %>% # 1 preset grouper, 1 user-defined summarise(Count = n(), # 1 preset summary, 1 user defined !

问题 I have a simple problem with non-standard evaluation: passing a variable name as an argument into a function. As a reproducible example, here's a simple thing: taking the mean of one variable, mpg from the mtcars dataset. My end goal is to have a function where I can input the dataset and the variable, and get the mean. So without a function: library(tidyverse) mtcars %>% summarise(mean = mean(mpg)) #> mean #> 1 20.09062 I've tried to use get() for non-standard evaluation, but I'm getting

问题 I have a simple problem with non-standard evaluation: passing a variable name as an argument into a function. As a reproducible example, here's a simple thing: taking the mean of one variable, mpg from the mtcars dataset. My end goal is to have a function where I can input the dataset and the variable, and get the mean. So without a function: library(tidyverse) mtcars %>% summarise(mean = mean(mpg)) #> mean #> 1 20.09062 I've tried to use get() for non-standard evaluation, but I'm getting

问题 I would like to check if the strings below are valid mathematical expressions: s1 = 'sin(x)' s2 = 'sin(x*m)' s3 = 'sin' s4 = 'sin(xm)' By 'valid', I mean the expression is a combination of operators (must be used in conjunction with variables or constants) variables x and/or m constants. By this definition s1 and s2 are valid while s3 and s4 are not. To identify if a string is valid, I wrote a function checkFxn that first attempts to convert the string into a call or one of its parts. If

问题 I'm a bit surprised by R's behaviour in a very specific case. Let's say I define a function square that returns the square of its argument, like this: square <- function(x) { return(x^2) } I want to call this function within another function, and I also want to display its name when I do that. I can do that using deparse(substitute()) . However, consider the following examples: ds1 <- function(x) { print(deparse(substitute(x))) } ds1(square) # [1] "square" This is the expected output, so all

问题 The new curly curly method of tidy evaluation is explained in this article. Several examples are given demonstrating the use of this style of non-standard evaluation (NSE). library(tidyverse) # Example 1 -------------------------- max_by <- function(data, var, by) { data %>% group_by({{ by }}) %>% summarise(maximum = max({{ var }}, na.rm = TRUE)) } starwars %>% max_by(height) starwars %>% max_by(height, by = gender) # Example 2 -------------------------- summarise_by <- function(data, ..., by

问题 I am trying to use data.table within a user facing function in a package I'm working on. I would like this function to behave as data.table -like as possible. This means for example that my function also features a by argument, which is passed to the underlying data.table call within the function. The user should be free to pass anything into "my" by which is possible directly in a data.table . Citing from ?data.table this includes: A single unquoted column name: e.g., DT[, .(sa=sum(a)), by=x

问题 Let's define: f <- function(x) deparse(substitute(x)) The challenge: find <something> so that f(<something>) returns "abc" . Excluding, of course, f(abc) . With "tidy NSE", i.e. quasiquoting, this is very easy. However, according to the NSE references (1, 2, 3), it is impossible since substitute is a pure quoting (as opposed to quasiquoting) function. I wonder if there is anything obscure or undocumented (not that uncommon!) that allows to unquote in substitute , hence the challenge. 回答1:

问题 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

问题 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