R help - Jul 2007 - problem assigning to indexed data frame element

Hi All,

Sorry if I ask an obvious thing, I am still new to R ...

I created a data frame of given dimensions to which I gave strings as
column names. I want to write to elements of the data frame by indexing
them with the row number and column name (string). The problem is that I
can read elements from the data frame in this way, but I cannot assign
to elements in this way. Instead, I get the following error message:

Error in Summary.factor(..., na.rm = na.rm) : 
        min not meaningful for factors

Please find the code I used farther below. It would be great if someone
could help me.

Best regards, Michael

PS: Coincidentally, I found this same error message mentioned in another
context (levelplot) as indicating a bug (original bug report PR# 6005 on
Mon, 22 Dec 2003)

------------------------
Michael Drescher
Ontario Forest Research Institute
Ontario Ministry of Natural Resources
1235 Queen St East
Sault Ste Marie, ON, P6A 2E3
Tel: (705) 946-7406
Fax: (705) 946-2030

------------------------

Code:
> sfalls.plot.comp <- matrix(nrow=plot.count, ncol=spec.count, byrow=T)
> colnames(sfalls.plot.comp) <- levels(SPECIES)
### SPECIES, SPP_VOL, & PLOT are columns/variables in a previously read
data file
> sfalls.plot.comp <- data.frame(sfalls.plot.comp)
> attach(sfalls.plot.comp)
> sfalls.plot.comp[is.na(sfalls.plot.comp)] <- 0
> sfalls.plot.comp
  Bf Bw Pj Po Sb
1  0  0  0  0  0
2  0  0  0  0  0
> hh <- 1
> current.spec <- SPECIES[hh]; current.vol <- SPP_VOL[hh]; current.plot
<- PLOT[hh]
> current.spec
[1] Bf
Levels: Bf Bw Pj Po Sb
> current.vol
[1] 2
> current.plot
[1] 1
> sfalls.plot.comp[current.plot,current.spec]
### thus, reading from the data frame in this way (using the column
name/string) works fine
[1] 0
> sfalls.plot.comp[current.plot,current.spec] <- current.vol	### but
assigning in this way does not work
Error in Summary.factor(..., na.rm = na.rm) : 
        min not meaningful for factors
> sfalls.plot.comp[current.plot,1] <- current.vol
### assigning by using the column number instead of the column name of
course does work
> sfalls.plot.comp[current.plot,current.spec]
[1] 2
> sfalls.plot.comp[current.plot,"Bw"] <- current.vol
### as does assigning when replacing 'current.spec' for its assigned
value in quotes, e.g., "Bw"
> sfalls.plot.comp[current.plot,"Bw"]
[1] 2
> sfalls.plot.comp
  Bf Bw Pj Po Sb
1  2  2  0  0  0
2  0  0  0  0  0

Check what is happening with current.spec.  It looks
to me as if you are trying to use a factor as an
index.  See below

--- "Drescher, Michael (MNR)"
<michael.drescher at ontario.ca> wrote:
> Hi All,
> 
> Sorry if I ask an obvious thing, I am still new to R
> ...
> 
> I created a data frame of given dimensions to which
> I gave strings as
> column names. I want to write to elements of the
> data frame by indexing
> them with the row number and column name (string).
> The problem is that I
> can read elements from the data frame in this way,
> but I cannot assign
> to elements in this way. Instead, I get the
> following error message:
> 
> Error in Summary.factor(..., na.rm = na.rm) : 
>         min not meaningful for factors
> 
> Please find the code I used farther below. It would
> be great if someone
> could help me.
> 
> Best regards, Michael
> 
> PS: Coincidentally, I found this same error message
> mentioned in another
> context (levelplot) as indicating a bug (original
> bug report PR# 6005 on
> Mon, 22 Dec 2003)
> 
> ------------------------
> Michael Drescher
> Ontario Forest Research Institute
> Ontario Ministry of Natural Resources
> 1235 Queen St East
> Sault Ste Marie, ON, P6A 2E3
> Tel: (705) 946-7406
> Fax: (705) 946-2030
> 
> ------------------------
> 
> Code:
> > sfalls.plot.comp <- matrix(nrow=plot.count,
> ncol=spec.count, byrow=T)
> > colnames(sfalls.plot.comp) <- levels(SPECIES)
> ### SPECIES, SPP_VOL, & PLOT are columns/variables
> in a previously read
> data file
> > sfalls.plot.comp <- data.frame(sfalls.plot.comp)
> > attach(sfalls.plot.comp)
> > sfalls.plot.comp[is.na(sfalls.plot.comp)] <- 0
> 
> > sfalls.plot.comp
>   Bf Bw Pj Po Sb
> 1  0  0  0  0  0
> 2  0  0  0  0  0
> 
> > hh <- 1
> > current.spec <- SPECIES[hh]; current.vol <-
> SPP_VOL[hh]; current.plot
> <- PLOT[hh]
> 
> > current.spec
> [1] Bf
> Levels: Bf Bw Pj Po Sb
> 
> > current.vol
> [1] 2
> 
> > current.plot
> [1] 1
> 
> > sfalls.plot.comp[current.plot,current.spec]
> ### thus, reading from the data frame in this way
> (using the column
> name/string) works fine
> [1] 0
> 
> > sfalls.plot.comp[current.plot,current.spec] <-
> current.vol	### but
> assigning in this way does not work
> Error in Summary.factor(..., na.rm = na.rm) : 
>         min not meaningful for factors
If I am reading this correctly 
current.spec is not a column name or a number. It is a
factor as the levels indicate.  You might be able to
get around this by  

current.spec <- as.character(SPECIES[hh])

R has,what to me is, an annoying tendency to read in
many columns of characters as factors.  This can be
changed by changing something in the startup file.
Exactly what I have forgotten.
> 
> > sfalls.plot.comp[current.plot,1] <- current.vol
> ### assigning by using the column number instead of
> the column name of
> course does work
> > sfalls.plot.comp[current.plot,current.spec]
> [1] 2
> 
> > sfalls.plot.comp[current.plot,"Bw"] <- current.vol
> ### as does assigning when replacing 'current.spec'
> for its assigned
> value in quotes, e.g., "Bw"
> > sfalls.plot.comp[current.plot,"Bw"]
> [1] 2
> 
> > sfalls.plot.comp
>   Bf Bw Pj Po Sb
> 1  2  2  0  0  0
> 2  0  0  0  0  0
> 
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