Using tryCatch in a for loop

Tue, May 22, 2018 1:42 PM

No. If your ouput is a numeric "matrix", it cannot include alpha. Columns
in a data frame can be of different classes, but each column must be single
class.

and finally, of course, see ?cat -- I think you are misusing it. If you
simply want to return "somestuff", your function should be:

function(w) {"somestuff"}

not

function(w) {cat("somestuff")}

As usual, apologies if I have misunderstood. Caveat emptor.

Cheers,
Bert



Bert Gunter

"The trouble with having an open mind is that people keep coming along and
sticking things into it."
-- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )

On Tue, May 22, 2018 at 1:11 PM, Bailey Hewitt <bailster at hotmail.com> wrote:

Data and code as promised:

#Creating a test dataset
Year<- c(2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010,
2011, 2012, 2013, 2014)
Lake1<- c(2, 4, 5, 2, 1, 1, 2, 3, 4, 5, 6, 2, 3, 1, 2)
Lake2<- c(1, 3, -1, 4, -2, 1, 2, 3, 4, 5, 6, 2, 3, 1, 2)
Lake3<- c(1, 2, 5, -3, 1, 1, 2, 3, 4, 5, 6, 2, 3, 1, 2)
Lake4<- c(1, 1, 1, 1, 1, 1, 1, 250, 240, 240, 240, 240, 240, 239, 255)
mydata<- data.frame(Year, Lake1, Lake2, Lake3, Lake4)

#Running a for loop that indicates when an error or warning occurs
y<- mydata[,2:5]
year <- mydata$Year
regimeshift <- data.frame()
for (i in 1:4){
  tryCatch({
    y.val <- y[,i]
    lin.reg <- lm(y.val~year, mydata)
    seg.reg <- segmented.lm(lin.reg, seg.Z = ~ year, psi = NA, control =
seg.control(stop.if.error = FALSE, n.boot = 0, it.max = 20))
    RSyear <- summary(seg.reg)$psi [1,2]
    SlopeRegime1 <- summary(seg.reg)$coefficients[2,1]
    SlopeDiff <- summary(seg.reg)$coefficients[3,1]
    new.regimeshift <- data.frame(RSyear=RSyear,
SlopeRegime1=SlopeRegime1, SlopeDiff=SlopeDiff)
    rownames(new.regimeshift) <- colnames(y)[i]
    regimeshift <- rbind(regimeshift,new.regimeshift)
    print(regimeshift)
  }, error= function(e) {cat("Error", "\n")},
    warning= function(w) {cat("Warning", "\n")})
}

Bailey




From: Daniel Nordlund <djnordlund at gmail.com>
Sent: May 22, 2018 3:06 PM
To: Bailey Hewitt; Bert Gunter
Cc: r-help at R-project.org
Subject: Re: [R] Using tryCatch in a for loop


On 5/22/2018 11:32 AM, Bailey Hewitt wrote:

Hi Bert,

Thank you for the quick response!

In its current state the code prints three lines that say "warning".

What I was expecting is that I would get a matrix with 4 columns, 1. column
names (from the original data, ex. Lake1) 2. breakpoint year 3. slope 4.
slope difference from the first to the second  segment of the segmented
regression. Each row in the matrix would be the results of the segmented
regression test for each lake in the original data frame, so Lake1 results
would be in row 2 (row 1 would be titles) and so on. If any of this is
confusing please  let me know and I will clarify!

Thanks!

Bailey




From: Bert Gunter <bgunter.4567 at gmail.com>
Sent: May 22, 2018 2:13 PM
To: Bailey Hewitt
Cc: r-help at R-project.org
Subject: Re: [R] Using tryCatch in a for loop




Others may have greater insight, but my response is: Exactly what did or

didn't happen that makes you say the code didn't work? That is, what did or
didn't you get when you ran it compared to your expectations?

  Cheers,
  Bert






Bert Gunter

"The trouble with having an open mind is that people keep coming along

and sticking things into it."

-- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )


On Tue, May 22, 2018 at 10:55 AM, Bailey Hewitt  <bailster at hotmail.com>

wrote:

  Hello All,

I have been trying to use a for loop to run segmented regressions

(from R package segmented) on many columns  of data in a data frame with
the end goal of writing a new file with the following columns: column
title, breakpoint year, slope, and difference  in  slope. Unfortunately,
when one of the columns doesn't have a breakpoint the code stops and
provides an error or warning. I would like the loop to keep running
regardless of the error/warning but I want it to write that it did
encounter an error or warning.   Based on my needs I found that tryCatch
appears to do what I need. I have looked at multiple examples, blogs, etc.
as well as gone over the documentation and Hadley Wickham's document in
Advanced R but I am still a novice when it comes to coding and I am
having   a hard time getting the code to work properly. Below is the code I
have developed thus far (with a test dataset as an example):

#Creating a test dataset
Year<- c(2000, 2001, 2002, 2003, 2004)
Lake1<- c(2, 4, 5, 2, 1)
Lake2<- c(1, 3, -1, 4, -2)
Lake3<- c(1, 2, 5, -3, 1)
mydata<- data.frame(Year, Lake1, Lake2, Lake3)

#Running a for loop that indicates when an error or warning occurs
y<- mydata[,2:4]
year <- mydata$Year
regimeshift <- data.frame()
for (i in 1:3){
   tryCatch({
     y.val <- y[,i]
     lin.reg <- lm(y.val~year, mydata)
     seg.reg <- segmented.lm(lin.reg, seg.Z = ~ year, psi = NA, control

= seg.control(stop.if.error = FALSE, n.boot = 0, it.max = 20))

     RSyear <- summary(seg.reg)$psi [1,2]
     SlopeRegime1 <- summary(seg.reg)$coefficients[2,1]
     SlopeDiff <- summary(seg.reg)$coefficients[3,1]
     new.regimeshift <- data.frame(RSyear=RSyear,

SlopeRegime1=SlopeRegime1, SlopeDiff=SlopeDiff)

     rownames(new.regimeshift) <- colnames(y)[i]
     regimeshift <- rbind(regimeshift,new.regimeshift)
     print(regimeshift)
   }, error= function(e) {cat("Error", "\n")},
     warning= function(w) {cat("Warning", "\n")})
}

Any ideas or suggestions you might have are greatly appreciated!

Bailey Hewitt
PhD Candidate
York University
Ontario, Canada

My suggestion is that you get your code to work on a single iteration
before running in a loop and wrapping the code in tryCatch

I ran your "set-up" code (before the loop).  then extracted your code
from the loop, set i <- 1, and then ran the code.  Here is what I got:

 > i <- 1
 >     y.val <- y[,i]
 >     lin.reg <- lm(y.val~year, mydata)
 >     seg.reg <- segmented.lm(lin.reg, seg.Z = ~ year, psi = NA,

control = seg.control(stop.if.error = FALSE, n.boot = 0, it.max = 20))
Warning message:
No breakpoint estimated

 >     RSyear <- summary(seg.reg)$psi [1,2]
 >     SlopeRegime1 <- summary(seg.reg)$coefficients[2,1]
 >     SlopeDiff <- summary(seg.reg)$coefficients[3,1]

Error in summary(seg.reg)$coefficients[3, 1] : subscript out of bounds

 >     new.regimeshift <- data.frame(RSyear=RSyear,

SlopeRegime1=SlopeRegime1, SlopeDiff=SlopeDiff)
Error in data.frame(RSyear = RSyear, SlopeRegime1 = SlopeRegime1,
SlopeDiff = SlopeDiff) :
   object 'SlopeDiff' not found

 >     rownames(new.regimeshift) <- colnames(y)[i]

Error in rownames(new.regimeshift) <- colnames(y)[i] :
   object 'new.regimeshift' not found

 >     regimeshift <- rbind(regimeshift,new.regimeshift)

Error in rbind(regimeshift, new.regimeshift) :
   object 'new.regimeshift' not found

 >     print(regimeshift)

the immediate problems that show up are
1.  there is no variable psi the summary(seg.reg) object (RSyear is NULL).
2.  the coefficients[] matrix in the summary(seg.reg) object does not
have 3 rows, so you get an error and SlopeDiff is not created.

You need to correct these problems, and any others, so that your code
runs correctly when there are no data problems.  Then you can worry
about trapping errors in the case where there are data problems.

Hope this is helpful,

Dan

--
Daniel Nordlund
Port Townsend, WA  USA

Using tryCatch in a for loop

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