[R] print and lapply....

[akshay kulkarni]

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 <ruipbarradas using sapo.pt>
Sent: Tuesday, November 8, 2022 12:24 AM
To: akshay kulkarni <akshay_e4 using hotmail.com>; R help Mailing list <r-help using r-project.org>
Subject: Re: [R] print and lapply....

�s 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 <ruipbarradas using sapo.pt>
> Sent: Monday, November 7, 2022 11:59 PM
> To: akshay kulkarni <akshay_e4 using hotmail.com>; R help Mailing list <r-help using r-project.org>
> Subject: Re: [R] print and lapply....
>
> �s 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]]
>>
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> 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


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