I was going through swirl() again as a refresher, and I've noticed that the author of swirl says the command ?matrix is the correct form to calling for a help screen. But, when I run ?matrix(), it still works? Is there a difference between having and not having a pair of parenthesis?
It's not specific to the swirl environment (about which I was entirely unaware until 5 minutes ago) That is standard for R. The help page for the ? shortcut says:
Arguments
topic
Usually, a name or character string specifying the topic for which help is sought.
Alternatively, a function call to ask for documentation on a corresponding S4 method: see the section on S4 method documentation. The calls pkg::topic and pkg:::topic are treated specially, and look for help on topic in package pkg.
It something like the second option that is being invoked with the command:
?matrix()
Since ?? is actually a different shortcut one needs to use this code to bring up that page, just as one needs to use quoted strings for help with for, if, next or any of the other reserved words in R:
?'?' # See ?Reserved
This is not based on a "fuzzy logic" search in hte help system. Using help instead of ? gets a different response:
> help("str()")
No documentation for ‘str()’ in specified packages and libraries:
you could try ‘??str()’
You can see the full code for the ? function by typing ? at the command line, but I am just showing how it starts the language level processing of the expressions given to it:
`?`
function (e1, e2)
{
if (missing(e2)) {
type <- NULL
topicExpr <- substitute(e1)
}
#further output omitted
By running matrix and in general any_function you get the source code of it.
Related
warning: I'm pretty new to R, sniny and co ==> I don't realize whether this question is interesting.
update : It turns out that it is a shiny question and it seems to be a frequent problem, that is not obvious. Please read all answers, they don't address the same cases.
I have a Data base in DB. Is there a difference between DBtoto <- reactive({DB()}) and DBtoto <- reactive({DB}) ? If so, what is it ?
In fact I don't see what BD() (with parentheses) means.
Yes, there's a difference. DB() is a call to the function named DB. DB is the function itself. If it's not a function, then DB() doesn't make sense, and will trigger a run-time error (unless there's another object somewhere which is a function).
reactive() is a Shiny function, that says the value of its argument may change over time. Usually it would make more sense to think the value of the function call would change, but it's (remotely) possible that the function itself could change.
I also found the first answer of What is “object of type ‘closure’ is not subsettable” error in Shiny? addresses this question. To summary, everything created with 'reactive()' in shiny must be referred as a function.
In my example, if DB was reactive (for instance DB <- reactive(read_DataBase())), then DB() must be referred with parenthesis. For instance, to get the attribute 'x', you must write BD()$x. In my 'DBtoto' example above the first expression holds in the case DB is itself reactive.
I'm trying to package some code I use for data analysis so that other workers can use it. Currently, I'm stuck trying to write a simple function that imports data from a specific file type generated by a datalogger and trims it for use by other functions. Here's the code:
import<-function(filename,type="campbell",nprobes){
if (filename==TRUE){
if (type=="campbell"){
message("File import type is from Campbell CR1000")
flux.data<<-read.table(filename,sep=",",header=T,skip=1)
flux.data<<-flux.data[,-c(1,2)];flux.data<<-flux.data[-c(1,2),]
if (nprobes=="missing"){
nprobes<-32
}
flux.data<<-flux.data[,c(1:nprobes)]
flux.data.names<<-colnames(flux.data) #Saves column names
}
}
}
Ideally, the result would be a dataframe/matrix flux.data and a concomittant vector/list of the preserved column headers flux.data.names. The code runs and the function executes without errors, but the outputs aren't preserved. I usually use <<- to get around the function enclosure but its not working in this case - any suggestions?
I think the real problem is that I don't quite understand how enclosures work, despite a lot of reading... should I be using environment to assign environments within the function?
User joran answered my question in the comments above:
The critical issue was just in how the function was written: the conditional at the start (if filename==TRUE) was intended to see if filename was specified, and instead was checking to see if it literally equaled TRUE. The result was the conditional never being met, and no function output. Here's what fixed it:
import<-function(filename,type="campbell",nprobes){
if (exists(filename){
if (type=="campbell"){
#etc....
Another cool thing he pointed out was that I didn't need the <<- operator to utilize the function output and instead could write return(flux.data). This is a much more flexible approach, and helped me understand function enclosures a lot better.
I have been using jsonlite to make REST GET calls. The number of parameters have increased and I am wondering how to make a REST POST call using R.
Per your request ...
library(jsonlite)
BLUF
Instead of
fromJSON(myurl, ...)
you need to call httr::POST directly:
txt <- httr::POST(myurl, ...)
fromJSON(txt)
Explanation
The basic mechanism for using jsonlite::fromJSON is to pass it a string. In the special case that you pass an URL (regexpr: ^https?://), it does you a courtesy by calling httr::GET and taking its output as your intended input. You can see this intent by looking at its source by typing in jsonlite::fromJSON and finding the line with if(grepl("^https?://" ...; if you try to find the function download_raw, you'll not find immediately since it is an un-exported function. You can find it as jsonlite:::download_raw (notice the third colon).
Looking at that function's source, you'll see that it makes direct calls to httr::GET. You can mimic how download_raw is calling httr::GET, modifying the arguments as needed. (It might be informative to look at both help(httr::GET) and help(httr::POST) and look for the differences between them. Spoiler: look at the body argument, potentially a list for keys/values. The examples are helpful.)
Now I'm making an endless runner where objects are spawned in front on me randomly.
I was told to make a spawnController and globalController object, so I did. Then this code should be put in the controller under step event
if(tick = 32)
{
tick = 0;
instance_create(room_width,room_height,random(spike,groundBlock));
instance_create(room_width,irandom_range(0,room_height-32));
}
tick += 1;
Is there anything wrong with it because i get an error, which is:
In object spawnController, event Step, action 1 at line 4: Wrong number of arguments to function or script.
instance_create(room_width,irandom_range(0,room_height-32));
The error messages in GM can sometimes be a bit unclear.. But in this case it was pretty clear. It goes about this line. And one of the scripts has too few arguments. Either irandom_range or instance_create you forgot an argument.
irandom_range takes two arguments to make a random number, so that is correct.
instance_create however takes 3 arguments: x,y position and the object from which you wish to create an instance. You're simply missing that argument (and the error tells you that). I think that is a typo as you do it correctly in the creation above.
Manual about instance_create
You have a syntax error here:
instance_create(room_width,irandom_range(0,room_height-32);
There's no closing parentheses or a 3rd argument.
One thing that stood out to me is that you used random instead of choose. Im not sure there is a difference in this situation, but choose allows you to list as many arguments you want.
But the other thing as was pointed out, was that your missing the object you want the 4th life to create. You need to specify what object you want it to make.
instance_create(room_width, irandom_range(0,room_height-32), OBJECT);
I don't know what is happening, but I can't seem to add a constant to a vector. For example, typing in the console c(1,2,3,4)+5 returns 15 instead of (6,7,8,9). What am I doing wrong?
Thank you for your help.
Someone.... probably you ... has redefined the "+" function. It's easy to do:
> `+` <- function(x,y) sum(x,y)
> c(1,2,3,4)+5
[1] 15
It's easy to fix, Just use rm():
> rm(`+`)
> c(1,2,3,4)+5
[1] 6 7 8 9
EDIT: The comments (which raised the alternate possibility that c had instead been redefined as sum) are prompting me to add information about how to examine and recover from the alternative possibilities. You could use two methods to determine which of the two functions in the expression c(1,2,3,4) + 5 was the culprit. One could either type their names (with the backticks enclosing +), and note whether you got the proper definition:
> `+`
function (e1, e2) .Primitive("+")
> c
function (..., recursive = FALSE) .Primitive("c")
Using rm on the culprit (the on that doesn't match above) remains the quickest solution. Using a global rm is an in-session brainwipe:
rm(list=ls())
# all user defined objects, including user-defined functions will be removed
The advice to quit and restart would not work in some situations. If you quit-with-save, the current function definitions would be preserved. If you had earlier quit-with-save from a session where the redefinition occurred, then not saving in this session would not have fixed the problem, either. The results of prior session are held in a file named ".Rdata and this file is invisible for both Mac and Windows users because the OS file viewer (Mac's Finder.app or MS's Windows Explorer) will not display file names that begin with a "dot". I suspect that Linux users get to see them by default since using ls in a Terminal session will show them. (It's easy to find ways to change that behavior in a Mac, and that is the way I run my device.) Deleting the .Rdata file is helpful in this instance, as well as in the situation where your R session crashes on startup.