I am writing my first R function.
IMDBmovierating <- function(movie){
link <- paste("http://www.omdbapi.com/?t=", movie, "&y=&plot=short&r=json", `sep = "")`
jsonData <- fromJSON(link)
df <- data.frame(jsonData)
}
And then nothing happens. Suspect it has something to do with return being needed. Not sure how I would write this.
To return df, simply write return(df):
IMDBmovierating <- function(movie){
link <- paste("http://www.omdbapi.com/?t=", movie, "&y=&plot=short&r=json", sep = "")
jsonData <- fromJSON(link)
df <- data.frame(jsonData)
return(df)
}
or, even simpler in this case, omit the last assignment:
IMDBmovierating <- function(movie){
link <- paste("http://www.omdbapi.com/?t=", movie, "&y=&plot=short&r=json", sep = "")
jsonData <- fromJSON(link)
data.frame(jsonData)
}
If the last expression evaluates to a result object, as data.frame(..) does, then this gets the return object of the enclosing expression and the explicit return statement may be omitted.
edit: and remove the back-ticks before sep and after you closing parenthesis
edit2: Of course MrFlick's comment is correct: the only thing really wrong with your code are the back-ticks that probably are simply a typo here on the site. Even the assignment produces the assigned value as a result object, but it is invisible. Hence, you can assign it, but it is not automatically printed on the console.
You simply need to evaluate the object at the end of your function so it will return a value. See the simple example below:
funA <- function(x) {
a <- x
}
funB <- function(x) {
b <- x
b
}
funA(1) # prints nothing
funB(1) # prints 'b'
[1] 1
EDIT:
As #MrFlick points out, both funA and funB return the evaluation of the last expression, but funA will not print anything. However, if you assign the output of funA(1) an object, that object will produce the value 1:
z <- funA(1)
z
[1] 1
z == funB(1)
[1] TRUE
The moral of the story is that you either need to assign the output of IMDBmovierating to an object, or explicitly evaluate df at the end of the function.
Looks like you just had a few typos.
Try this and dont forget to include your library to help people out when answering you. :)
library(RJSONIO)
IMDBmovierating <- function(movie){
link <- paste("http://www.omdbapi.com/?t=", movie,"&y=&plot=short&r=json", sep = "")
jsonData <- fromJSON(link)
df <- data.frame(jsonData)
}
test <- IMDBmovierating(1984)
test
Related
I am working on a function that tries to give me the top answers of a column. In the example below there is just a part of my whole function. My final goal is to run the function over a loop. I have detected something weird: why is print(df_col_indicator) gonna change the result when I define "df_col_indicator" externally and not within my function? With print(df_col_indicator) my function is actually exactly doing what I want..
library(dplyr)
library(tidyverse)
remove(list = ls())
dataframe_test <- data.frame(
county_name = c("a", "b","c", "d","e", "f", "g", "h"),
column_test1 = c(100,100,100,100,100,100,50,50),
column_test2 = c(40,90,50,40,40,100,13,14),
column_test3 = c(100,90,50,40,30,40,100,50),
month = c("2020-09-01", "2020-09-01" ,"2020-09-01" ,"2020-09-01" ,"2020-09-01" ,"2020-09-01" ,"2020-08-01","2020-08-01"))
choose_top_5 <- function(df, df_col_indicator, df_col_month, char_month, numb_top, df_col_county) {
### this here changes output of my function
#print(df_col_indicator) # changes output of my function depending on included or excluded
### enquo / ensym / deparse
df_col_indicator_ensym <- ensym(df_col_indicator)
df_col_month_ensym <- ensym(df_col_month)
### filter month and top 5 observations
df_top <- df %>%
filter(!!df_col_month_ensym == char_month) %>%
slice_max(!!df_col_indicator_ensym, n = numb_top) %>%
select(!!df_col_county, !!df_col_month_ensym, !!df_col_indicator_ensym)
return(df_top)
}
### define "df_col_indicator" within the function
a = choose_top_5(df = dataframe_test, df_col_indicator = "column_test3",
df_col_month = "month", char_month = "2020-09-01", numb_top = 5,
df_col_county = "county_name")
a
### define "df_col_indicator" externally
external = "column_test3"
b = choose_top_5(df = dataframe_test, df_col_indicator = external,
df_col_month = "month", char_month = "2020-09-01", numb_top = 5,
df_col_county = "county_name")
b
### goal is to run function over loop
external <- c("column_test1","column_test2","column_test3")
my_list <- list()
for (i in external) {
my_list[[i]] <- choose_top_5(df = dataframe_test, df_col_indicator = i,
df_col_month = "month", char_month = "2020-09-01", numb_top = 5,
df_col_county = "county_name")
}
my_list
Your example is quite lengthy. Let's boil it down to a minimal reproducible example with two very similar functions. These both take a single argument and simply print the passed variable to the console, and return the result of calling ensym on the same variable.
The only difference between the two is the order in which the calls to print and ensym are made.
library(rlang)
test_ensym1 <- function(x)
{
result <- ensym(x)
print(x)
return(result)
}
test_ensym2 <- function(x)
{
print(x)
result <- ensym(x)
return(result)
}
Now we might expect these two functions to do exactly the same thing, and indeed when we pass a string directly to them, they both give the same result:
test_ensym1("hello")
#> [1] "hello"
#> hello
test_ensym2("hello")
#> [1] "hello"
#> hello
But look what happens when we use an external variable to pass in our string:
y <- "hello"
test_ensym1(y)
#> [1] "hello"
#> y
test_ensym2(y)
#> [1] "hello"
#> hello
The functions both still print "hello", as expected, but they return a different result. When we called ensym first, the function returned the symbol y, and when we called print first it returned the symbol hello.
The reason for this is that when you call a function in R, the symbols you pass as parameters are not evaluated immediately. Instead, they are interpreted as promise objects and evaluated as required in the body of the function. It is this lazy evalutation that allows for some of the tidyverse trickery.
The difference between the two functions above is that calling print(x) forces the evaluation of x. Before that point, x is an unevaluated symbol. Afterwards, it behaves just like any other variable you would use interactively in the console, so when you call ensym, you are calling it on this evaluated variable, not as an unevaluated promise.
ensym, on the other hand, does not evaluate x, so if ensym is called first, it will return the unevaluated symbol that was passed to the function.
So actually, the easiest way to fix your problem is to move print to after the ensym call.
You also have to change ensym to as.symbol.
Consider a function like this
f <- function(x) ensym(x)
myvar <- "some string"
You will find that
> f("some string")
`some string`
> f(myvar)
myvar
This is because ensym only searches for the thing one step ahead. It attempts to convert whatever thing found into a symbol and just returns that (note that if what found is neither a string nor variable, then you will get an error). As such, in your first example, ensym returns column_test3; in your second one, it returns external.
As far as I can tell, what you want to do is getting the value that df_col_indicator represents and then converting that value into a symbol. This means you have to first evaluate df_col_indicator and then convert. as.symbol does what you need.
g <- function(x) as.symbol(x)
myvar <- "some string"
Some tests
> g("some string")
`some string`
> g(myvar)
`some string`
I'm sure this question may have been asked already, but I couldnt find an answer to my satisfaction.
So my Problem I defined a function (See below) which should take a Variable (x) and check if its part of a dataframe (y). The function should than ask for a promt until it is part of said dataframe.
However when I let it run it wont overwrite the variable inside the function so that the global enviroment variable gets also changed.
Thus var1 should store the value I gave through the prompt inside the function.
Thx :)
#Function
fn_Valid_prompt <- function(x, y, boolOP= FALSE){
while(is.element(x, colnames(y)) == boolOP){
cat("A")
x <<- readline(prompt="Please enter variable: ")
}
if (is.element(x, colnames(y)) != boolOP){
cat(green(bold("Success!")))}
}
#
var1 <- "V1"
data <- c(1:9)
metadata <- as.data.frame(matrix(data,3,3))
fn_Valid_prompt(var1, metadata, boolOP= FALSE)
The following version works, although i'm not sure of your intent with this code :
#Function
fn_Valid_prompt <- function(x, y, boolOP= FALSE){
while(is.element(x, colnames(y)) == boolOP){
x <- readline(prompt="Please enter variable: ")
}
if (is.element(x, colnames(y)) != boolOP){
cat("Success!")}
return(x)
}
#
var1 <- "V1"
data <- c(1:9)
metadata <- as.data.frame(matrix(data,3,3))
result = fn_Valid_prompt("V10", metadata, boolOP= FALSE)
cat(result)
Your mistake was to use <<- instead of <-. Furthermore, i assume you wanted to return the result ?
Imagine you have a simple function that specifies which statistical tests to run for each variable. Its syntax, simplified for the purposes of this question is as follows:
test <- function(...) {
x <- list(...)
return(x)
}
which takes argument pairs such as Gender = 'Tukey', and intends to pass its result to other functions down the line. The output of test() is as follows:
test(Gender = 'Tukey')
# $Gender
# [1] "Tukey"
What is desired is the ability to replace the literal Gender by a dynamically assigned variable varname (e.g., for looping purposes). Currently what happens is:
varname <- 'Gender'
test(varname = 'Tukey')
# $varname
# [1] "Tukey"
but what is desired is this:
varname <- 'Gender'
test(varname = 'Tukey')
# $Gender
# [1] "Tukey"
I tried tinkering with functions such as eval() and parse(), but to no avail. In practice, I resolved the issue by simply renaming the resulting list, but it is an ugly solution and I am sure there is an elegant R way to achieve it. Thank in advance for the educational value of your answer.
NB: This question occurred to me while trying to program a custom function which uses mcp() from the effects package in its internals. The said mcp() function is the real world counterpart of test().
EDIT1: Perhaps it needs to be clarified that (for educational purposes) changing test() is not an option. The question is about how to pass the tricky argument to test(). If you take a look at NB, it becomes clear why: the real world counterpart of test(), namely mcp(), comes with a package. And while it is possible to create a modified copy of it, I am really curious whether there exists a simple solution in somehow 'converting' the dynamically assigned variable to a literal in the context of dot-arguments.
This works:
test <- function(...) {
x = list(...)
names(x) <- sapply(names(x),
function(p) eval(as.symbol(p)))
return(x)
}
apple = "orange"
test(apple = 5)
We can use
test <- function(...) {
x <- list(...)
if(exists(names(x))) names(x) <- get(names(x))
x
}
test(Gender = 'Tukey')
#$Gender
#[1] "Tukey"
test(varname = 'Tukey')
#$Gender
#[1] "Tukey"
What about this:
varname <- "Gender"
args <- list()
args[[varname]] <- "Tukey"
do.call(test, args)
I have below function. I cannot alter the function in any way except the first block of code in the function.
In this simple example I want to display apply some function on returning object.
The point is the name of variable returned by function may vary and I'm not able to guess it.
Obviously I also cannot wrap the f function into { x <- f(); myfun(x); x }.
The below .Last.value in my on.exit call represents the value to be returned by f function.
f <- function(param){
# the only code I know - start
on.exit(if("character" %in% class(.Last.value)) message(print(.Last.value)) else message(class(.Last.value)))
# the only code I know - end
# real processing of f()
a <- "aaa"
"somethiiiing"
if(param==1L) return(a)
b <- 5L
"somethiiiing"
if(param==2L) return(b)
"somethiiiing"
return(32)
}
f(1L)
# function
# [1] "aaa"
f(2L)
# aaa
# [1] 5
f(3L)
# integer
# [1] 32
Above code with .Last.value seems to be working with lag (so in fact not working) and also the .Last.value is probably not the way to go as I want to use the value few times like if(fun0(x)) fun1(x) else fun2(x), and because returned value might be a big object, copy it on the side is also bad approach.
Any way to use on.exit or any other function which can help me to run my function on the f function results without knowing result variable name?
In a similar way to how you are modifying the function, you could easily wrap it as well. Here's a reproducible example.
library(data.table)
append.log<-function(x) {
cat(paste("value:",x,"\n"))
}
idx.dt <- data.table:::`[.data.table`
environment(idx.dt)<-asNamespace("data.table")
idx.wrap <- function(...) {
x<-do.call(idx.dt, as.list(substitute(...())), envir=parent.frame())
append.log(if(is(x, "data.table")) {
nrow(x)
} else { NA })
x
}
environment(idx.wrap)<-asNamespace("data.table")
(unlockBinding)("[.data.table",asNamespace("data.table"))
assign("[.data.table",idx.wrap,envir=asNamespace("data.table"),inherits=FALSE)
dt<-data.table(a=1:10, b=seq(2, 20, by=2), c=letters[1:10])
dt[a%%2==0]
Since R 3.2.0 it is fully possible, thanks to new function returnValue.
Working example below.
f <- function(x, err = FALSE){
pt <- proc.time()[[3L]]
on.exit(message(paste("proc.time:",round(proc.time()[[3L]]-pt,4),"\nnrow:",as.integer(nrow(returnValue()))[1L])))
Sys.sleep(0.001)
if(err) stop("some error")
return(x)
}
dt <- data.frame(a = 1:5, b = letters[1:5])
f(dt)
f(dt, err=T)
f(dt)
f(dt[dt$a %in% 2:3 & dt$b %in% c("c","d"),])
I'm trying to change the name of a variable that is included inside a for loop and function call. In the example below, I'd like column_1 to be passed to the plot function, then column_2 etc. I've tried using do.call, but it returns "object 'column_j' not found". But object column_j is there, and the plot function works if I hard-code them in. Help much appreciated.
for (j in 2:12) {
column_to_plot = paste("column_", j, sep = "")
do.call("plot", list(x, as.name(column_to_plot)))
}
I do:
x <- runif(100)
column_2 <-
column_3 <-
column_4 <-
column_5 <-
column_6 <-
column_7 <-
column_8 <-
column_9 <-
column_10 <-
column_11 <-
column_12 <- rnorm(100)
for (j in 2:12) {
column_to_plot = paste("column_", j, sep = "")
do.call("plot", list(x, as.name(column_to_plot)))
}
And I have no errors. Maybe you could provide hard-code which (according to your question) works, then will be simpler to find a reason of the error.
(I know that I can generate vectors using loop and assign, but I want to provide clear example)
You can do it without the paste() command in your for loop. Simply assign the columns via the function colnames() in your loop:
column_to_plot <- colnames(dataframeNAME)[j]
Hope that helps as a first kludge.
Are you trying to retrieve an object in the workspace by a character string? In that case, parse() might help:
for (j in 2:12) {
column_to_plot = paste("column_", j, sep = "")
plot(x, eval(parse(text=column_to_plot)))
}
In this case you could use do.call(), but it would not be required.
Edit: wrapp parse() in eval()
Here is one way to do it:
tmp.df <- data.frame(col_1=rnorm(10),col_2=rnorm(10),col_3=rnorm(10))
x <- seq(2,20,by=2)
plot(x, tmp.df$col_1)
for(j in 2:3){
name.list <- list("x",paste("col_",j,sep=""))
with(tmp.df, do.call("lines",lapply(name.list,as.name))) }
You can also do colnames(tmp.df)[j] instead of paste(..) if you'd like.