I have created some sequentially named variable i.e holder1, holder2, holder3, which contain single strings I would like to pass to grep
However I am having trouble getting the holder variables to return their values rather than just their names when I pass it to grep, my current attempt looks like:
vec<-c("str1","str2","str3","str4")
for(i in 1:length(vec)){
assign(paste("holder",i,sep=""),vec[i])
positions[i]<-grep( eval (paste ("holder",i,sep="")) ,colnames(df),ignore.case=TRUE)
}
This will search for holder1 within the colnames of df, which is not what I want, I would like to search for the contents of holder i within the df i.e str1 str2 e.t.c.
Any help greatly appreciated!
Solved it with eval and parse:
for(i in 1:length(vec)){
assign(paste("holder",i,sep=""),vec[i])
print ( paste ("holder",i,sep="") )
positions<-c(positions,grep( eval( parse(text= paste ("holder",i,sep="")) ),colnames(data),ignore.case=TRUE))
}
Related
Very green R user here. Sorry if this is asked and answered somewhere else, I haven't been able to find anything myself.
I can't figure out why I can't get a for loop to work define multiple new dataframes but looping through a predefined list.
My list is defined from a subset of variable names from an existing dataframe:
varnames <- colnames(dplyr::select(df_response, -1:-4))
Then I want to loop through the list to create a new dataframe for each variable name on the list containing the results of summary function:
for (i in varnames){
paste0("df_",i) <- summary(paste0("df$",i))
}
I've tried variations with and without paste function but I can't get anything to work.
paste0 returns a string. Both <- and $ require names, but you can use assign and [[ instead. This should work:
varnames <- colnames(dplyr::select(df_response, -1:-4))
for (i in varnames){
assign(
paste0("df_", i),
summary(df[[i]])
)
}
Anyway, I'd suggest working with a list and accessing the summaries with $:
summaries <- df_response |>
dplyr::select(-(1:4)) |>
purrr::imap(summary)
summaries$firstvarname
I have multiple dataframes and would like to remove the first row in all of them.
I have tried using a for loop but cannot understand what I am doing wrong
for (i in cities){
i <- i[-1, ]
}
I get the following error code:
Error in i[-1, ] : incorrect number of dimensions
If we assume that the only objects in your workspace are dataframes then this might succeed:
cities <- objects() )
for (i in cities) { assign(i, get(i)[-1,])}
Explanation:
Two thing wrong with original codes:
One was already mentioned in comments. "df" is not the same as df. You need to use get to convert a character value to a "true" R name that is used to retrieve an object having that name. The result of object() is only a character value. In R the term "name" means a "language object". See the help page: ?mode. (There is potential confusion about rownames and columnnames which are always "character"-class.) It's not like SAS which is a macro language that has no such distinction.
The second error was trying to get substitution for the i on the left-hand side of <-. The would have failed even if you were working with actual R names. The assign function is designed to handle character values that are then converted to R names.
say you get a list of all the tables in your environment, and you call that list cities. You can't just iterate over each value of cities and change things, because in the list they are just characters.
Here is what you need:
for (i in cities){
tmp <- get(i) # load the actual table
tmp <- tmp[-1, ] # remove first column
assign(i, tmp) # re-assign table to original table name
}
I have matlab files with an integer in each name of my variables inside (except the first one). I want to loop to concatenate the name of the integers.
There is my code:
library('R.matlab')
mat <- readMat('SeriesContPJM.mat')
#str(mat)
#typeof(mat)
#mat[[1]]
write.csv(mat$vol.PJM$data[[4]][[1]], "PJM.csv")
i = 2
while (i < 7)
{
write.csv(get(paste("mat$vol.PJM", as.character(i), "$data[[4]][[1]]", sep = "")), paste(paste("PJM", as.character(i), sep="_"), "csv", sep ="."))
i = i + 1
}
I have write.csv(mat$vol.PJM$data[[4]][[1]], "PJM.csv") which gives me the good ouput. I would like the same for the other variable names in the loop but I get the following ouput:
+ Error in get(paste("mat$vol.PJM", as.character(i), "$data[[4]][[1]]", (from importpjm.R#10) :
objet 'mat$vol.PJM2$data[[4]][[1]]' introuvable
"introuvable" means "not found" in French.
Here you're mixing where you need to use get and where you need to use eval(parse()).
You can use get with a string variable game, e.g., get("mtcars"), but [ is a function that needs to be evaluated.
get("mtcars[2, 2]") won't work because you don't have a variable named "mtcars[2, 2]", you have a variable named "mtcars" and a function named "[" that can take arguments 2, 2.
eval(parse(text = "mtcars[2, 2]")) will work because it doesn't just look for a variable, it actually evaluates the text string as if you typed it into the command line.
So, you could rewrite your loop, replacing the get(...) with eval(parse(text = ...)) and it would probably work, assuming the strings you've pasted together have the right syntax. But this can be difficult to read and debug. In 6 months, if you look back at this code and need to understand it or modify it, it will be confusing.
Another way to do it would be to use [[ with strings to extract sublists. Rather than mess with eval(parse()) I would do this:
vols = paste0("vol.PJM", 2:7)
for (vol in vols) {
write.csv(mat[[vol]][["data"]][[4]][[1]],
paste0(vol, ".csv"))
}
I think it's more readable, and it's easy to debug the vols vector beforehand to make sure all your names are correct. Similarly, if you want to loop over all elements, you could initialize the vols as something like names(mat), or use some sort of regex criteria to extract the appropriate sublists from names(mat).
I have written a loop in R. The code is expected to go through a list of variables defined in a list and then for each of the variables perform a function.
Problem 1 - I cannot loop through the list of variables
Problem 2 - I need to insert each output from the values into Mongo DB
Here is an example of the list:
121715771201463_626656620831011
121715771201463_1149346125105084
Based on this value - I am running a code and i want this output to be inserted into MongoDB. Right now only the first value and its corresponding output is inserted
test_list <-
C("121715771201463_626656620831011","121715771201463_1149346125105084","121715771201463_1149346125105999")
for (i in test_list)
{ //myfunction//
mongo.insert(mongo, DBNS, i)
}
I am able to only pick the values for the first value and not all from the list
Any help is appreciated.
Try this example, which prints the final characters
myfunction <- function(x){ print( substr(x, 27, nchar(x)) ) }
test_list <- c("121715771201463_626656620831011",
"121715771201463_1149346125105084",
"121715771201463_1149346125105999")
for (i in test_list){ myfunction(i) }
for (j in 1:length(test_list)){ myfunction(test_list[j]) }
The final two lines should each produce
[1] "31011"
[1] "105084"
[1] "105999"
It is not clear whether "variable" is the same as "value" here.
If what you mean by variable is actually an element in the list you construct, then I think Ilyas comment above may solve the issue.
If "variable" is instead an object in the workspace, and elements in the list are the names of the objects you want to process, then you need to make sure that you use get. Like this:
for(i in ls()){
cat(paste(mode(get(i)),"\n") )
}
ls() returns a list of names of objects. The loop above goes through them all, uses get on them to get the proper object. From there, you can do the processing you want to do (in the example above, I just printed the mode of the object).
Hope this helps somehow.
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
How to name variables on the fly in R?
I have 10 objects of type list named: list1, list2, ..., list10. And I wanted to use the output from my function FUN to replace the first index of these list variables through a for loop like this:
for (i in 1:10){
eval(parse(test=(paste("list",i,sep=""))))[[1]] <- FUN()
}
but this does not work. I also used lapply in this way and again it is wrong:
lapply(eval(parse(text=(paste("list",i,sep=""))))[[1]], FUN)
Any opinion would be appreciated.
This is FAQ 7.21. The most important part of that FAQ is the last part that says not to do it that way, but to put everything into a list and operate on the list.
You can put your objects into a list using code like:
mylists <- lapply( 1:10, function(i) get( paste0('list',i) ) )
Then you can do the replacement with code like:
mylists <- lapply( mylists, function(x) { x[[1]] <- FUN()
x} )
Now if you want to save all the lists, or delete all the lists, you just have a single object that you need to work with instead of looping through the names again. If you want to do something else to each list then you just use lapply or sapply on the overall list in a single easy step without worrying about the loop. You can name the elements of the list to match the original names if you want and access them that way as well. Keeping everything of interest in a single list will also make your code safer, much less likely to accidentilly overwrite or delete another object.
You probably want something like
for (i in 1:10) {
nam <- paste0("list", i) ## built the name of the object
tmp <- get(nam) ## fetch the list by name, store in tmp
tmp[[1]] <- FUN() ## alter 1st component of tmp using FUN()
assign(nam, value = tmp) ## assign tmp back to the current list
}
as the loop.