[datatable-help] data.table on existing data.frame list

[Matthew Dowle]

Hi,

When the file contains the column names (as is best practice) then any 
text after the last column is read (such as comments) is ignored (with 
warning is intended).  Some improvement here could be made but comments 
in large files isn't something that's come up before. fread isn't a drop 
in replacement for read.table yet, but it would be good if it was.

If fread is reading your comments into a column,  then I guess the first 
row is data row and the last column contains the comments. Just delete 
the comments afterwards using DT[,lastcolumn:=NULL]. Or include column 
names in the file.

To hard-name columns, can use setnames() afterwards (either to rename 
old to new names, or to overwrite whatever names are there, if any).

If you want to read a subset of columns, use 'select' argument.

The plan is to create a wrapper for fread that can be used as a drop in 
replacement for read.table.

Are your files large and did you create them or are they given?

Matthew

On 05/08/13 19:18, iembry wrote:
> Hi Matthew, thank you for your prompt response.
>
> I am experimenting with fread and I am having a problem with comments not
> being ignored. In read.table, I can ignore the comments and create column
> names. I have not seen any way to either create column names or ignore
> comments within the fread function.
>
> How would I use fread to both ignore the comments and also to add column
> names as I can with read.table?
>
> ratingdepostlistedread <- fread("03217500.exsa.rdb", sep="auto",
> sep2="auto", header="auto", na.strings="NA", stringsAsFactors=FALSE,
> verbose=FALSE))
>
>
> ratingdepostlisted <- read.table("03217500.exsa.rdb", sep = "\t", fill =
> TRUE, comment.char = "#", header = T, as.is = TRUE, stringsAsFactors =
> FALSE, na.strings = "NA", col.names = c("y", "shift", "x", "stor")
>
>
> Thank you.
>
> Irucka
>
>
>
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