Skip to content

Problem when index is given by a changing formula in loop - BUG??

2 messages · greatest.possible.newbie, R. Michael Weylandt

Original
greatest.possible.newbie
# 
Dear community,

I have a little problem filling in a vector with loop output.
I think the problem is the following: I am caluclating the index which
indicates where the loop output should be placed at by a formula. But when I
want to fill in or read out some specific index places this doesn't work
properly. Let me show you my code:

# CODE
################
ln_0 <- 0
ln_max <- 20
ln_schritt <- 0.1
l_frak_0 <- 25
g_l_frak_0 <- 0.5
ln_auslastung <- 2

l_frak <- rep(0, 1+(ln_max-ln_0)/ln_schritt)
ln <- ln_0

while (ln < (ln_max+ln_schritt))
{
  insert <- 1+ (ln-ln_0)/ln_schritt
  l_frak[insert] <-  100
#l_frak_0 / g_l_frak_0 + floor(ln/ln_auslastung) * l_frak_0/g_l_frak_0 *
(1-g_l_frak_0)  -  l_frak_0 * (1-g_l_frak_0) * ln
# for simplification I replace the real formula by 100  

  ln <- ln + ln_schritt
}
names(l_frak) <- seq(ln_0, ln_max, ln_schritt)
#names(l_frak) <- c(1:length(l_frak))
l_frak[which(l_frak[]==0)]
# 0.7  1.2 18.9 
#  0    0    0
# The places in the vector where the filling in doesn't work: 
# 8   13   190

# Now try the following:
#################
ln <- 0.7
insert <- 1+ (ln-ln_0)/ln_schritt
insert
# [1] 8
# BUT:
l_frak[insert]
# 0.6
#  10
# But it should yield
l_frak[8]
# 0.7
#   0
#########
# END CODE

When I change the mode of the variable "insert" to numeric this doesn't
change anything. When I change it to
as.numeric(as.character(1+ (ln-ln_0)/ln_schritt))
Then the place where the filling in doesn't work is at
9.9 or at the 100th
place of the vector.

Is this a bug??

Thank you for your help,
Daniel 


--
View this message in context: http://r.789695.n4.nabble.com/Problem-when-index-is-given-by-a-changing-formula-in-loop-BUG-tp4630492.html
Sent from the R help mailing list archive at Nabble.com.
R. Michael Weylandt
# 
No it's not a bug in R.

Indexing can only occur by integers so there's an automatic conversion
to integer inside of `[`. Your "insert" variable is actually slightly
less than 8 (note as.integer(insert) == 7) by some amount that's too
small to print, but the computer still picks up on.

More concretely:

x <- 1:10

x[2]
x[3]
x[2.2]
x[2.8]
x[2.999999]

x[insert]
x[as.integer(insert)]
x[round(insert)]

Hopefully that helps clear things up,

Michael

On Fri, May 18, 2012 at 7:50 AM, greatest.possible.newbie
<daniel.hoop at gmx.net> wrote: