R help - Feb 2013 - How does this function print, why is n1 which equals 1 printed as 2?

Windows 7, R 2.12.1
Colleagues,
I am trying to understand the n.for.2means function. The code below is a copy of
the function (renamed to n.for.2means.js). I have inserted a single line of code
towards the bottom of the function which uses the cat function to print the
value of n1. You will note the value (preceded by stars) is printed as 1.
The function (1) prints a lot of output without any instructions in the function
to print anything (other than the cat statement I added), and when it prints (2)
reports the value of n1 to be 2!.
I have two questions, (i) how is the function printing when there is no code to
print and (ii) how is n1 which equals 1 being reported as 2? I suspect there is
something fundamental about R that I don't know.
Thank you for the help.
John
 
 
library(epicalc)
n.for.2means.js <- function (mu1, mu2, sd1, sd2, ratio = 1, alpha = 0.05,
power = 0.8)
{
  n1 <- (sd1^2 + sd2^2/ratio) * (qnorm(1 - alpha/2) - qnorm(1 - 
power))^2/(mu1 - mu2)^2
  n1 <- round(n1)
  n2 <- ratio * n1
  if (length(alpha) == 1) {
    alpha1 <- NULL
  }
  else {
    alpha1 <- alpha
  }
  if (length(power) == 1) {
    power1 <- NULL
  }
  else {
    power1 <- power
  }
  if (length(ratio) == 1) {
    ratio1 <- NULL
  }
  else {
    ratio1 <- ratio
  }
  table1 <- cbind(mu1, mu2, sd1, sd2, n1, n2, alpha1, power1, 
                  ratio1)
  colnames(table1)[colnames(table1) == "alpha1"] <-
"alpha"
  colnames(table1)[colnames(table1) == "power1"] <-
"power"
  colnames(table1)[colnames(table1) == "ratio1"] <-
"n2/n1"
  table1 <- as.data.frame(table1)
  cat("******n1*******=",n1,"\n")
  returns <- list(mu1 = mu1, mu2 = mu2, sd1 = sd1, sd2 = sd2, 
                  alpha = alpha, n1 = n1, n2 = n2, power = power, ratio = ratio,
                  table = table1)
  class(returns) <- c("n.for.2means", "list")
  returns
}
n.for.2means.js(0,8,10/6,10/6)
 
 
John David Sorkin M.D., Ph.D.
Chief, Biostatistics and Informatics
University of Maryland School of Medicine Division of Gerontology
Baltimore VA Medical Center
10 North Greene Street
GRECC (BT/18/GR)
Baltimore, MD 21201-1524
(Phone) 410-605-7119
(Fax) 410-605-7913 (Please call phone number above prior to faxing)
Confidentiality Statement:
This email message, including any attachments, is for the sole use of the
intended recipient(s) and may contain confidential and privileged information. 
Any unauthorized use, disclosure or distribution is prohibited.  If you are not
the intended recipient, please contact the sender by reply email and destroy all
copies of the original message.

On 13-02-01 8:47 AM, John Sorkin wrote:
> Windows 7, R 2.12.1
> Colleagues,
> I am trying to understand the n.for.2means function. The code below is a
copy of the function (renamed to n.for.2means.js). I have inserted a single line
of code towards the bottom of the function which uses the cat function to print
the value of n1. You will note the value (preceded by stars) is printed as 1.
> The function (1) prints a lot of output without any instructions in the
function to print anything (other than the cat statement I added), and when it
prints (2) reports the value of n1 to be 2!.
> I have two questions, (i) how is the function printing when there is no
code to print and (ii) how is n1 which equals 1 being reported as 2? I suspect
there is something fundamental about R that I don't know.
I haven't run the code, but presumably it's just the usual auto 
printing.  Unless a function sets the result to be invisible, results
of functions are printed by calling print() after they are returned.

Since your function returns something with class

c("n.for.2means", "list")

R will look for a print method for those classes, and use it to print 
the result.  There's no print.list method in standard R; it just uses 
the default.  But there's probably a print.n.for.2means function in the 
package (possibly not exported; you might need 
epicalc:::print.n.for.2means to see it).  There might be a print.list 
function there instead or as well.

Duncan Murdoch
> Thank you for the help.
> John
>
>
> library(epicalc)
> n.for.2means.js <- function (mu1, mu2, sd1, sd2, ratio = 1, alpha =
0.05, power = 0.8)
> {
>    n1 <- (sd1^2 + sd2^2/ratio) * (qnorm(1 - alpha/2) - qnorm(1 - 
power))^2/(mu1 - mu2)^2
>    n1 <- round(n1)
>    n2 <- ratio * n1
>    if (length(alpha) == 1) {
>      alpha1 <- NULL
>    }
>    else {
>      alpha1 <- alpha
>    }
>    if (length(power) == 1) {
>      power1 <- NULL
>    }
>    else {
>      power1 <- power
>    }
>    if (length(ratio) == 1) {
>      ratio1 <- NULL
>    }
>    else {
>      ratio1 <- ratio
>    }
>    table1 <- cbind(mu1, mu2, sd1, sd2, n1, n2, alpha1, power1,
>                    ratio1)
>    colnames(table1)[colnames(table1) == "alpha1"] <-
"alpha"
>    colnames(table1)[colnames(table1) == "power1"] <-
"power"
>    colnames(table1)[colnames(table1) == "ratio1"] <-
"n2/n1"
>    table1 <- as.data.frame(table1)
>    cat("******n1*******=",n1,"\n")
>    returns <- list(mu1 = mu1, mu2 = mu2, sd1 = sd1, sd2 = sd2,
>                    alpha = alpha, n1 = n1, n2 = n2, power = power, ratio =
ratio,
>                    table = table1)
>    class(returns) <- c("n.for.2means", "list")
>    returns
> }
> n.for.2means.js(0,8,10/6,10/6)
>
>
> John David Sorkin M.D., Ph.D.
> Chief, Biostatistics and Informatics
> University of Maryland School of Medicine Division of Gerontology
> Baltimore VA Medical Center
> 10 North Greene Street
> GRECC (BT/18/GR)
> Baltimore, MD 21201-1524
> (Phone) 410-605-7119
> (Fax) 410-605-7913 (Please call phone number above prior to faxing)
> Confidentiality Statement:
> This email message, including any attachments, is for the sole use of the
intended recipient(s) and may contain confidential and privileged information. 
Any unauthorized use, disclosure or distribution is prohibited.  If you are not
the intended recipient, please contact the sender by reply email and destroy all
copies of the original message.
>
>
>
> ______________________________________________
> R-help at r-project.org mailing list
> 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.
>

On Feb 1, 2013, at 7:47 AM, John Sorkin wrote:
> Windows 7, R 2.12.1
> Colleagues,
> I am trying to understand the n.for.2means function. The code below  
> is a copy of the function (renamed to n.for.2means.js). I have  
> inserted a single line of code towards the bottom of the function  
> which uses the cat function to print the value of n1. You will note  
> the value (preceded by stars) is printed as 1.
> The function (1) prints a lot of output without any instructions in  
> the function to print anything (other than the cat statement I  
> added), and when it prints (2) reports the value of n1 to be 2!.
> I have two questions, (i) how is the function printing when there is  
> no code to print and (ii) how is n1 which equals 1 being reported as  
> 2? I suspect there is something fundamental about R that I don't know.
1) on my machine the output from the cat() call is:

******n1*******= 1

2) All of the "output without any instructions in the function to  
print anything"  is just the value of the list object from the  
function. Unless you return values using the `invisible` function, any  
user define function executed at the console will print its value.  
That is standard interactive session behavior. So one gets after the  
the cat output:

$mu1
[1] 0

$mu2
[1] 8

$sd1
[1] 1.666667

$sd2
[1] 1.666667

$alpha
[1] 0.05

$n1
[1] 1

$n2
[1] 1

$power
[1] 0.8

$ratio
[1] 1

$table
   mu1 mu2      sd1      sd2 n1 n2
1   0   8 1.666667 1.666667  1  1

attr(,"class")
[1] "n.for.2means" "list"


-- 
David.
> Thank you for the help.
> John
>
>
> library(epicalc)
> n.for.2means.js <- function (mu1, mu2, sd1, sd2, ratio = 1, alpha =  
> 0.05, power = 0.8)
> {
>  n1 <- (sd1^2 + sd2^2/ratio) * (qnorm(1 - alpha/2) - qnorm(1 -   
> power))^2/(mu1 - mu2)^2
>  n1 <- round(n1)
>  n2 <- ratio * n1
>  if (length(alpha) == 1) {
>    alpha1 <- NULL
>  }
>  else {
>    alpha1 <- alpha
>  }
>  if (length(power) == 1) {
>    power1 <- NULL
>  }
>  else {
>    power1 <- power
>  }
>  if (length(ratio) == 1) {
>    ratio1 <- NULL
>  }
>  else {
>    ratio1 <- ratio
>  }
>  table1 <- cbind(mu1, mu2, sd1, sd2, n1, n2, alpha1, power1,
>                  ratio1)
>  colnames(table1)[colnames(table1) == "alpha1"] <-
"alpha"
>  colnames(table1)[colnames(table1) == "power1"] <-
"power"
>  colnames(table1)[colnames(table1) == "ratio1"] <-
"n2/n1"
>  table1 <- as.data.frame(table1)
>  cat("******n1*******=",n1,"\n")
>  returns <- list(mu1 = mu1, mu2 = mu2, sd1 = sd1, sd2 = sd2,
>                  alpha = alpha, n1 = n1, n2 = n2, power = power,  
> ratio = ratio,
>                  table = table1)
>  class(returns) <- c("n.for.2means", "list")
>  returns
> }
> n.for.2means.js(0,8,10/6,10/6)
>
>
> John David Sorkin M.D., Ph.D.
> Chief, Biostatistics and Informatics
> University of Maryland School of Medicine Division of Gerontology
> Baltimore VA Medical Center
> 10 North Greene Street
> GRECC (BT/18/GR)
> Baltimore, MD 21201-1524
> (Phone) 410-605-7119
> (Fax) 410-605-7913 (Please call phone number above prior to faxing)
> Confidentiality Statement:
> This email message, including any attachments, is for ...{{dropped:15}}