Às 19:22 de 07/11/2022, akshay kulkarni escreveu:
Dear Rui,
THanks for your reply...The point is the loop is a scraping
code, and in your examples you have assumed that the body acts on i, the loop
variable. Can you adapt your code to JUST PRINT the loop variable i ?
By the by, I think I have stumbled upon the answer: The lapply() caches the
result, and prints the output of the function in question immediately after
printing the final i. The i's get printed serially, as the function
progresses....
lapply(1:4,function(x){print(x);Sys.sleep(x^2);x^2})
[1] 1
[1] 2
[1] 3
[1] 4
[[1]]
[1] 1
[[2]]
[1] 4
[[3]]
[1] 9
[[4]]
[1] 16
Here x^2 's print only after 4 is printed on the console....
tHanks anyways for your reply....
THanking you,
Yours sincerely,
AKSHAY M KULKARNI
________________________________
From: Rui Barradas <ruipbarra...@sapo.pt>
Sent: Tuesday, November 8, 2022 12:24 AM
To: akshay kulkarni <akshay...@hotmail.com>; R help Mailing list
<r-help@r-project.org>
Subject: Re: [R] print and lapply....
Às 18:33 de 07/11/2022, akshay kulkarni escreveu:
Dear Rui,
Actually, I am replacing a big for loop by the lapply()
function, and report the progress:
lapply(TP, function(i) { BODY; print(i)})
Can you please adjust your solution in this light?
THanking you,
Yours sincerely,
AKSHAY M KULKARNI
________________________________
From: Rui Barradas <ruipbarra...@sapo.pt>
Sent: Monday, November 7, 2022 11:59 PM
To: akshay kulkarni <akshay...@hotmail.com>; R help Mailing list
<r-help@r-project.org>
Subject: Re: [R] print and lapply....
Às 17:17 de 07/11/2022, akshay kulkarni escreveu:
Dear members,
I have the following code and output:
TP <- 1:4
lapply(TP,function(x){print(x);x^2})
[1] 1
[1] 2
[1] 3
[1] 4
[[1]]
[1] 1
[[2]]
[1] 4
[[3]]
[1] 9
[[4]]
[1] 16
How do I make the print function output x along with x^2, i.e not at the
beginning but before each of x^2?
Many thanks in advance....
THanking you,
Yours sincerely
AKSHAY M KULKARNI
[[alternative HTML version deleted]]
______________________________________________
R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
Hello,
Here are two options, with ?cat and with ?message.
TP <- 1:4
lapply(TP, function(x){
cat("x =", x, "x^2 =", x^2, "\n")
})
lapply(TP, function(x){
msg <- paste("x =", x, "x^2 =", x^2)
message(msg)
})
Hope this helps,
Rui Barradas
Hello,
What do you want the lapply loop to return? If you have a BODY doing
computations, do you want the lapply to return those values and report
the progress?
I have chosen cat or message over print because
- cat returns invisible(NULL),
- message returns invisible()
- print returns a value, what it prints.
Can you adapt the code below to your use case?
TP <- 1:4
lapply(TP, function(x, verbose = TRUE){
# BODY
y <- rnorm(100, mean = x)
# show progress
if(verbose)
cat("x =", x, "x^2 =", x^2, "\n")
#return value
c(x = x, mean = mean(y))
})
lapply(TP, function(x, verbose = TRUE){
# BODY
y <- rnorm(100, mean = x)
# show progress
if(verbose) {
msg <- paste("x =", x, "x^2 =", x^2)
message(msg)
}
#return value
c(x = x, mean = mean(y))
})
Hope this helps,
Rui Barradas
Hello,
No, the x^2 are not printed after the i's. The x^2 are the function's
return values. The function prints the i's, then returns x^2.
As for your problem, it is now more clerar.
I would write a function accepting a url to take care of scraping and
call it in the lapply loop. The progress report can be in the loop, like
below.
This is a complete working example, scraping the Wikipedia list of
countries by GDP. The urls are in a list (it's always the same, I'm not
complicating things) and in a real scraping function I would wrap
tryCatch around it, just in case.
First the function, then the urls list, then the lapply loop.
library(rvest)
scrape <- function(url) {
page <- read_html(url)
gdp <- page |>
html_element(".wikitable") |>
html_table() |>
as.data.frame()
names(gdp) <- unlist(gdp[1,, drop = TRUE])
gdp <- gdp[-1,]
row.names(gdp) <- NULL
#return value
gdp
}
wiki_gdp_url <-
"https://en.wikipedia.org/wiki/List_of_countries_by_GDP_(nominal)"
urls_list <- list(wiki_gdp_url, wiki_gdp_url)
TP <- seq_along(urls_list)
TP
# [1] 1 2
df_list <- lapply(TP, \(i) {
URL <- urls_list[[i]]
data <- scrape(URL)
# show progress
message("iteration: ", i)
#return value
data
})
str(df_list)
Hope this helps,
Rui Barradas
______________________________________________
R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
