[R] RODBC and Excel: Wrong Data Type Assumed on Import

[Earl F. Glynn]

The first column in my Excel sheet has mostly numbers but I need to treat it
as character data:

> library(RODBC)
> channel <- odbcConnectExcel("U:/efg/lab/R/Plasmid/construct list.xls")
> plasmid <- sqlFetch(channel,"Sheet1", as.is=TRUE)
> odbcClose(channel)

> names(plasmid)
[1] "Plasmid Number" "Plasmid"        "Concentration"  "Comments"
"Lost"

# How is the type decided?  I need a character type.
> class(plasmid$"Plasmid Number")
[1] "numeric"
> typeof(plasmid$"Plasmid Number")
[1] "double"

> plasmid$"Plasmid Number"[273:276]
[1] 274  NA  NA 276

The two NAs are supposed to be 275a and 275b.  I tried the "as.is=TRUE" but
that didn't help.

I consulted Section 4, Relational databases, in the R Data Import/Export
document (for Version 2.2.0).

Section 4.2.2, Data types, was not helpful.  In particular, this did not
seem helpful:  "The more comprehensive of the R interface packages hide the
type conversion issues from the user."

Section 4.3.2, Package RODBC, provided a "simple example of using ODBC ..
with a(sic) Excel spreadsheet" but is silent on how to control the data type
on import.  Could the documentation be expanded to address this issue?

I really need to show "Plasmid 275a" and "Plasmid 275b" instead of "Plasmid
NA".

Thanks for any help with this.

efg
--
Earl F. Glynn
Scientific Programmer
Bioinformatics Department
Stowers Institute for Medical Research