R help - Jul 2015 - problem with using seq() or rep() inside a for loop

Dear All:

I want to use seq() inside a for-loop and use the looping counter i as 
the "by" argument in seq(). Here is some exemplary data and code:

# set up some data
distances <- c(0, NA, NA, NA, NA, NA,
                5, 0, NA, NA, NA, NA,
                5, 2, 0, NA, NA, NA,
                18, 5, 5, 0, NA, NA,
                25, 10, 8, 1, 0, NA,
                41, 20, 18, 5, 2, 0)

MD_dist <- matrix(distances, ncol = 6)

MEAN <- numeric(nrow(MD_dist) - 1) # just to set up a vector

# loop to add (subsets of) off-diagonal diagonal values
for(i in 1: ncol(MD_dist) - 1){
diagonal <- as.vector(MD_dist[row(MD_dist) == (col(MD_dist) - i)])
# the following line extracts every i-th element from "diagonal"
diagonal.2 <- diagonal[seq(1, to = length(diagonal), by = i)]
MEAN[i] <- mean(diagonal.2)
}

However, I keep getting the following error message:

Error in seq.default(1, to = length(diagonal), by = i) :
   invalid (to - from)/by in seq(.)

May I add that if I run the loop "by hand" - i.e. by just setting i =
1,
2... etc and then running the core without the for {...} , everything 
works fine.

Further, when I use rep(..) instead of seq(...) to extract the desired 
values from "diagonal", I have the very same problem - it works
outside
a for loop, but fails inside.

I am using R 3.2.1. (x64) under Win 7 Professional on a 64 bit machine.

Any suggestion would be appreciated.

Thank you so much.

Karl

-- 
Karl Schilling

You need to put the expression on the right of the colon in your for
statement in parenthesis:

for (i in 1:(ncol(MD_dist) - 1)){
...
}

On 7 July 2015 at 19:00, Karl Schilling <karl.schilling at uni-bonn.de>
wrote:
> Dear All:
>
> I want to use seq() inside a for-loop and use the looping counter i as the
> "by" argument in seq(). Here is some exemplary data and code:
>
> # set up some data
> distances <- c(0, NA, NA, NA, NA, NA,
>                5, 0, NA, NA, NA, NA,
>                5, 2, 0, NA, NA, NA,
>                18, 5, 5, 0, NA, NA,
>                25, 10, 8, 1, 0, NA,
>                41, 20, 18, 5, 2, 0)
>
> MD_dist <- matrix(distances, ncol = 6)
>
> MEAN <- numeric(nrow(MD_dist) - 1) # just to set up a vector
>
> # loop to add (subsets of) off-diagonal diagonal values
> for(i in 1: ncol(MD_dist) - 1){
> diagonal <- as.vector(MD_dist[row(MD_dist) == (col(MD_dist) - i)])
> # the following line extracts every i-th element from "diagonal"
> diagonal.2 <- diagonal[seq(1, to = length(diagonal), by = i)]
> MEAN[i] <- mean(diagonal.2)
> }
>
> However, I keep getting the following error message:
>
> Error in seq.default(1, to = length(diagonal), by = i) :
>   invalid (to - from)/by in seq(.)
>
> May I add that if I run the loop "by hand" - i.e. by just setting
i = 1,
> 2... etc and then running the core without the for {...} , everything works
> fine.
>
> Further, when I use rep(..) instead of seq(...) to extract the desired
> values from "diagonal", I have the very same problem - it works
outside a
> for loop, but fails inside.
>
> I am using R 3.2.1. (x64) under Win 7 Professional on a 64 bit machine.
>
> Any suggestion would be appreciated.
>
> Thank you so much.
>
> Karl
>
> --
> Karl Schilling
>
> ______________________________________________
> R-help at 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.

The fact that it works when you pass your i values "by hand" should
alert you that perhaps your loop control does not do what you think it does.

Consider: 
Your version:
for(i in 1:6 - 1)

What you probably meant:
for(i in 1:(6 - 1)) print(i)

The error is created on the first iteration of your loop where you set i to 0.
"by" can't be 0.




Cheers,
Boris

On Jul 7, 2015, at 2:00 PM, Karl Schilling <karl.schilling at uni-bonn.de>
wrote:
> Dear All:
> 
> I want to use seq() inside a for-loop and use the looping counter i as the
"by" argument in seq(). Here is some exemplary data and code:
> 
> # set up some data
> distances <- c(0, NA, NA, NA, NA, NA,
>               5, 0, NA, NA, NA, NA,
>               5, 2, 0, NA, NA, NA,
>               18, 5, 5, 0, NA, NA,
>               25, 10, 8, 1, 0, NA,
>               41, 20, 18, 5, 2, 0)
> 
> MD_dist <- matrix(distances, ncol = 6)
> 
> MEAN <- numeric(nrow(MD_dist) - 1) # just to set up a vector
> 
> # loop to add (subsets of) off-diagonal diagonal values
> for(i in 1: ncol(MD_dist) - 1){
> diagonal <- as.vector(MD_dist[row(MD_dist) == (col(MD_dist) - i)])
> # the following line extracts every i-th element from "diagonal"
> diagonal.2 <- diagonal[seq(1, to = length(diagonal), by = i)]
> MEAN[i] <- mean(diagonal.2)
> }
> 
> However, I keep getting the following error message:
> 
> Error in seq.default(1, to = length(diagonal), by = i) :
>  invalid (to - from)/by in seq(.)
> 
> May I add that if I run the loop "by hand" - i.e. by just setting
i = 1, 2... etc and then running the core without the for {...} , everything
works fine.
> 
> Further, when I use rep(..) instead of seq(...) to extract the desired
values from "diagonal", I have the very same problem - it works
outside a for loop, but fails inside.
> 
> I am using R 3.2.1. (x64) under Win 7 Professional on a 64 bit machine.
> 
> Any suggestion would be appreciated.
> 
> Thank you so much.
> 
> Karl
> 
> -- 
> Karl Schilling
> 
> ______________________________________________
> R-help at 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.

for (i in 1:(ncol(MD_dist) - 1)){
   ...
   }

Even better, replace
   1:(n-1)
with
   seq_len(n-1)
The latter does what you want (and empty integer vector) when n is 1;
the former would give c(1,0).


Bill Dunlap
TIBCO Software
wdunlap tibco.com

On Tue, Jul 7, 2015 at 2:11 PM, David Barron <dnbarron at gmail.com>
wrote:
> You need to put the expression on the right of the colon in your for
> statement in parenthesis:
>
> for (i in 1:(ncol(MD_dist) - 1)){
> ...
> }
>
> On 7 July 2015 at 19:00, Karl Schilling <karl.schilling at
uni-bonn.de>
> wrote:
> > Dear All:
> >
> > I want to use seq() inside a for-loop and use the looping counter i as
> the
> > "by" argument in seq(). Here is some exemplary data and
code:
> >
> > # set up some data
> > distances <- c(0, NA, NA, NA, NA, NA,
> >                5, 0, NA, NA, NA, NA,
> >                5, 2, 0, NA, NA, NA,
> >                18, 5, 5, 0, NA, NA,
> >                25, 10, 8, 1, 0, NA,
> >                41, 20, 18, 5, 2, 0)
> >
> > MD_dist <- matrix(distances, ncol = 6)
> >
> > MEAN <- numeric(nrow(MD_dist) - 1) # just to set up a vector
> >
> > # loop to add (subsets of) off-diagonal diagonal values
> > for(i in 1: ncol(MD_dist) - 1){
> > diagonal <- as.vector(MD_dist[row(MD_dist) == (col(MD_dist) - i)])
> > # the following line extracts every i-th element from
"diagonal"
> > diagonal.2 <- diagonal[seq(1, to = length(diagonal), by = i)]
> > MEAN[i] <- mean(diagonal.2)
> > }
> >
> > However, I keep getting the following error message:
> >
> > Error in seq.default(1, to = length(diagonal), by = i) :
> >   invalid (to - from)/by in seq(.)
> >
> > May I add that if I run the loop "by hand" - i.e. by just
setting i = 1,
> > 2... etc and then running the core without the for {...} , everything
> works
> > fine.
> >
> > Further, when I use rep(..) instead of seq(...) to extract the desired
> > values from "diagonal", I have the very same problem - it
works outside a
> > for loop, but fails inside.
> >
> > I am using R 3.2.1. (x64) under Win 7 Professional on a 64 bit
machine.
> >
> > Any suggestion would be appreciated.
> >
> > Thank you so much.
> >
> > Karl
> >
> > --
> > Karl Schilling
> >
> > ______________________________________________
> > R-help at 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.
>
> ______________________________________________
> R-help at 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.
>
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