I'm new to R and studying how read_excel() and excel_sheets() work, trying to use two such codes below. These are intended to read the second sheet of an excel file.
output <- read_excel(excel_sheets("population.xlsx")[2],
path = "population.xlsx")
output <- read_excel(excel_sheets("population.xlsx"),
sheet = 2, path = "population.xlsx")
The first code runs successfully, but the second one doesn't with the error
Error: length(x) == 1L is not TRUE
I'd like to know the reason why
it happens and how I can fix it.
The document of read_excel says it can use 'sheet' argument to select which sheet to read, which I guess is identical to stating the number of the order of a character vector ( i.e. excel_sheets("population.xlsx")[2] in this case).
Just read_excel(path = "population.xlsx", sheet = 2) should work. Your first code is getting a list of all sheets and then selecting the name of the second; read_excel accepts both integer position and sheet names as the argument for sheet.
You may be confused because you need to know something about argument matching; named arguments are matched and then they are matched left to right. So in the first example, path is specified, and then the excel_sheets call is passed to the sheet argument. In the second, you specify sheet and so I think it will get passed to the range argument, which is supposed to only accept a character vector of length 1. That's the source of the error you have.
Related
In an R script, I assign a name to some data. The name depends on parameters. I do this using
number<-1
assign(paste("variable", as.character(number), sep=""),2)
The above accomplices the same as variable1<-2. Now I want to save the result for later
save(?,file=paste("variable",as.character(number),".RData",sep=""))
What code can go in the ? slot where it should say variable1 except I need to construct this name using paste or some similar technique. Simply putting get(paste("variable",as.character(number),".RData",sep="")) does not work.
save can also use list as parameter. According to ?save
list - A character vector containing the names of objects to be saved.
Thus, we specify the object name as a string (paste0('variable', number)) for the list argument and file as the one used by OP (or make it more concise with paste0 (as.character is not necessary as integer/numeric gets automatically convert to type character in paste
save(list = paste0('variable', number),
file = paste0("variable", number, ".RData"))
Check for the file created in the working directory
list.files(getwd(), pattern = '\\.RData$')
#[1] "variable1.RData"
I know there are ways to extract all arguments to a function using, for example, rlang::fn_fmls. But is it possible to extract the description of one of these arguments from the package documentation?
For example, what if I wanted to extract the description of the na.rm argument to base::sum()?
I'm imagining something like:
get_argument_description(fn = 'base::sum', arg = 'na.rm')
Return:
"logical. Should missing values (including NaN) be removed?"
You could try to read the associated help file for that function, and grep the line where \item{argument}. However, multi-line help texts are allowed, if the next line does not start with a \ you would want to grab that too.
This answer shows a way to acess the file, then it is just a matter of grabbing the correct line(s). I also want to highlight a different function in tools,
tools:::.Rd_get_text()
Which almost gets you where you want, (if you find the correct line)
library(tools)
db = Rd_db("base")
tools:::.Rd_get_text(x = db[["sum.Rd"]])[21] # 21 is the line you want here
[1] " na.rm: logical. Should missing values (including 'NaN') be removed?"
I have to use the code bellow but I don't completely understand how it works. Why it won't work if I change du.4 by du.f and then use the f when calling the function? For some reason it only works with numbers and I do not undarstand why.
This is the error that it is giving in the case of du.f
Error in paste("Meth1=", nr, ".ps", sep = "") : object 'f' not found
du.4 <- function(u,v,a){(exp(a)*(-1+exp(a*v)))/(-exp(a)+exp(a+a*u)-exp(a*(u+v))+exp(a+a*v))}
plotmeth1 <- function(data1,data2,alpha,nr) {
psfile <-paste("Meth1=",nr,".ps",sep="")
diffmethod <-paste("du.",nr,sep="")
title=paste("Family",nr)
alphavalue <-paste("alpha=",round(alpha,digits=3),sep="")
#message=c("no message")
postscript(psfile)
data3<-sort(eval(call(diffmethod,data1,data2,alpha)))
diffdata <-data3[!is.na(data3)]
#if(length(data3)>length(diffdata))
#{message=paste("Family ",nr,"contains NA!")}
tq <-((1:length(diffdata))/(length(diffdata)+1))
plot(diffdata,tq,main=title,xlab="C1[F(x),G(y)]",ylab="U(0,1)",type="l")
legend(0.6,0.3,c(alphavalue))
abline(0,1)
#dev.off()
}
In R, a dot is used as just another character in identifiers. It is often used for clarity but doesn't have a formal function in defining the part after the dot as being in a name-space given by the part of the identifier before the dot. In something like du.f you can't refer to the function by f alone, even if your computation is inside of an environment named du. You can of course define a function named du.4 and then use 4 all by itself, but when you do so you are using the number 4 as just a number and not as a reference to the function. For example, if
du.4 <- function(u,v,a){(exp(a)*(-1+exp(a*v)))/(-exp(a)+exp(a+a*u)-exp(a*(u+v))+exp(a+a*v))}
Then du.4(1,2,3) evaluates to 21.08554 but attempting to use 4(1,2,3) throws the error
Error: attempt to apply non-function
In the case of your code, you are using paste to assemble the function name as a string to be passed to eval. It makes sense to paste the literal number 4 onto the string 'du.' (since the paste will convert 4 to the string '4') but it doesn't make sense to paste an undefined f onto 'du.'. It does, however, make sense to paste the literal string 'f' onto 'du.', so that the function call plotmeth1 (data1, data2, alpha, 'f') will work even though plotmeth1 (data1, data2, alpha, f) will fail.
See this question for more about the use of the dot in R identifiers.
Why can't R find this variable?
assign(paste0('my', '_var'), 2)
get(paste0('my', '_var')) ## isn't this returning an object?
save(get(paste0('my', '_var')), file = paste0('my', '_var.RDATA'))
This throws the error:
Error in save(paste0("my", "_var"), file = paste0("my", "_var.RDATA")) :
object ‘paste0("my", "_var")’ not found
From the help page, the save() function expects "the names of the objects to be saved (as symbols or character strings)." Those values are not evaulated, ie you can't put in functions that will eventually return strings or raw values themselves. Use the list= parameter if you want to call a function to return a string the the name of a variable.
save(list=paste0('my', '_var'), file = paste0('my', '_var.RDATA'))
Though using get/assign is often not a good practice in R. They are usually better ways so you might want to rethink your general approach.
And finally, if you are saving a single object, you might want to consider saveRDS() instead. Often that's the behavior people are expecting when they use the save() function.
The documentation for save says that ... should be
the names of the objects to be saved (as symbols or character strings).
And indeed if you type save into the console you can see that the source has the line
names <- as.character(substitute(list(...)))[-1L]
where substitute captures its argument and doesn't evaluate it. So as the error suggests, it is looking for an object with the name paste0('my', '_var'), not evaluating the expressions supplied.
I have a large dataset (~ 200MB) stored in a .txt-file which I need to read into R. Unfortunately there are no separators (like " " or ",") between the values of the variables and there is no header file.
But there is a codebook, which gives the variable names and also specifies which column belongs to which variable. Some of the variable take one column of space, some take more (so read.fwf won't work); but their width is the same for all cases.
I possibly only have to read in a few of these variables, so I expect that I will just have to select the necessary columns and name the variables. What would be an elegant solution to do this (and maybe even preselect meaningful variable types)?
You can consider loading the data as is and then parsing each line using 'strsplit' with appropriate regular expression.
con <- file("yourfile.txt", open = "r")
lines <- readLines(con)
Iterate it over, apply strsplit to each line and add that to your data table with rbind.