Just got a call from a telecommuting colleague
who's using Ruby to automate a bunch of CEV[1]
CFD[2] simulations.
She says that she can't figure out how to /append/
to a CSV file using Ruby's standard library.
Does anyone have the magic recipe, or should
she be using FasterCSV instead?
Thanks,
--
Bil
http://fun3d.larc.nasa.gov
[1] CEV = Crew Exploration Vehicle
[2] CFD = Computational Fluid Dynamics
Bil Kleb wrote:
...
She says that she can't figure out how to /append/
to a CSV file using Ruby's standard library.
...
Wouldn't it just be a matter of opening the file in append mode?
cheers
Chris
Hi,
Bil Kleb wrote:
Just got a call from a telecommuting colleague
who's using Ruby to automate a bunch of CEV[1]
CFD[2] simulations.She says that she can't figure out how to /append/
to a CSV file using Ruby's standard library.Does anyone have the magic recipe, or should
she be using FasterCSV instead?
Please use CSV::Writer. An instance of CSV is not an IO in contrast to
a FasterCSV.
CSV::Writer.generate(file_to_append) do |csv|
csv << [1, 2, 3]
end
Regards,
// NaHi
Bil Kleb wrote:
...
She says that she can't figure out how to /append/
to a CSV file using Ruby's standard library.
...
Not sure if you read ruby-forum (http://www.ruby-forum.com/\)
but a response ther indicates that you can do this via the CSV::Writer:
File.open('csvout.csv', 'a'){ |outfile|
CSV::Writer.generate(outfile) do |csv|
csv << ['c1', nil, '', '"', "\r\n", 'c2']
end
}
Cheers
Chris
ChrisH wrote:
Bil Kleb wrote:
...She says that she can't figure out how to /append/
to a CSV file using Ruby's standard library....
Wouldn't it just be a matter of opening the file in append mode?
cheers
Chris
Ok, note to self "read docs before commenting"
it seems CSV only supports 'r','rb','w','wb' for open.
FasterCSV delegates to an IO object and supports all IO's modes.
So it would be the winner
Cheers
--
Posted via http://www.ruby-forum.com/\.
ChrisH wrote:
Bil Kleb wrote:
...She says that she can't figure out how to /append/
to a CSV file using Ruby's standard library....
Wouldn't it just be a matter of opening the file in append mode?
It would, but unfortunately CSV doesn't support 'a'
or 'a+', viz, lib/ruby/1.8/csv.rb,
83 def CSV.open(path, mode, fs = nil, rs = nil, &block)
84 if mode == 'r' or mode == 'rb'
85 open_reader(path, mode, fs, rs, &block)
86 elsif mode == 'w' or mode == 'wb'
87 open_writer(path, mode, fs, rs, &block)
88 else
89 raise ArgumentError.new("'mode' must be 'r', 'rb', 'w', or 'wb'")
90 end
91 end
Later,
--
Bil
http://fun3d.larc.nasa.gov
Interestingly, this design choice in FasterCSV has been questioned in the past. I just keep liking it more and more though as issues like this arise. 
James Edward Gray II
On Jul 12, 2006, at 1:55 PM, Chris Hulan wrote:
it seems CSV only supports 'r','rb','w','wb' for open.
FasterCSV delegates to an IO object and supports all IO's modes.
So it would be the winner
Bil Kleb wrote:
ChrisH wrote:
Bil Kleb wrote:
...She says that she can't figure out how to /append/
to a CSV file using Ruby's standard library....
Wouldn't it just be a matter of opening the file in append mode?
It would, but unfortunately CSV doesn't support 'a'
or 'a+', viz, lib/ruby/1.8/csv.rb,
Well, darn.
All I can think of offhand is 1) write the new stuff to a new file
and then 2) use fileutils to append the new file onto the old one.
Disclaimers:
1. I'm not sure fileutils has a good way to do that, but
if it doesn't, there's always system("cat newfile >>oldfile").
2. Obviously be sure the old file is closed before trying to
so anything funny with it.
Hal
I'm not very familiar with the CSV lib, but if the heart of the matter
is appending to a CSV file, you hardly need a full-on CSV lib for
something like that.
File.open(my_csv) {|f| f.puts new_record} # think it oughta be as
simple as that
File.open(my_csv) {|f| f.puts *new_records} # puts can take a list, too
Bil Kleb wrote:
ChrisH wrote:
> Bil Kleb wrote:
> ...
>> She says that she can't figure out how to /append/
>> to a CSV file using Ruby's standard library.
> ...
>
> Wouldn't it just be a matter of opening the file in append mode?It would, but unfortunately CSV doesn't support 'a'
or 'a+', viz, lib/ruby/1.8/csv.rb,83 def CSV.open(path, mode, fs = nil, rs = nil, &block)
84 if mode == 'r' or mode == 'rb'
85 open_reader(path, mode, fs, rs, &block)
86 elsif mode == 'w' or mode == 'wb'
87 open_writer(path, mode, fs, rs, &block)
88 else
89 raise ArgumentError.new("'mode' must be 'r', 'rb', 'w', or 'wb'")
90 end
91 endLater,
--
Bil
http://fun3d.larc.nasa.gov
Sorry about my last post sort of skipping over the whole matter of the
write mode.. you're smarter than me, though, I'm sure you'll be fine.
;-p
Bil Kleb wrote:
ChrisH wrote:
> Bil Kleb wrote:
> ...
>> She says that she can't figure out how to /append/
>> to a CSV file using Ruby's standard library.
> ...
>
> Wouldn't it just be a matter of opening the file in append mode?It would, but unfortunately CSV doesn't support 'a'
or 'a+', viz, lib/ruby/1.8/csv.rb,83 def CSV.open(path, mode, fs = nil, rs = nil, &block)
84 if mode == 'r' or mode == 'rb'
85 open_reader(path, mode, fs, rs, &block)
86 elsif mode == 'w' or mode == 'wb'
87 open_writer(path, mode, fs, rs, &block)
88 else
89 raise ArgumentError.new("'mode' must be 'r', 'rb', 'w', or 'wb'")
90 end
91 endLater,
--
Bil
http://fun3d.larc.nasa.gov
I haven't used the CSV module before either, but looking into it this
test script I came up with parses a CSV source file, writing it to a
new array. Then you can append to that new array and write the results
back to the original CSV file. It's not pretty and might not be the
most Rubyish way of getting the job done but it worked for me using
Ruby 1.8.2 on Win32. Try it out and let me know...
require 'csv'
# test.csv consists of three comma delimited fields, something like:
#
# 1,"Greg","Admin"
# 2,"Joe","User"
# 3,"Jim","Admin"
new_array =
temp_array =
reader = CSV.open('test.csv', 'r') do |row|
(0...row.nitems).each do |item|
temp_array.push(row[item].data)
end
new_array << temp_array
temp_array =
end
new_items = [4,"Jane","User"]
new_array << new_items
CSV.open('test.csv', 'w') do |writer|
new_array.each do |row|
writer << row
end
end
Bil Kleb wrote:
ChrisH wrote:
> Bil Kleb wrote:
> ...
>> She says that she can't figure out how to /append/
>> to a CSV file using Ruby's standard library.
> ...
>
> Wouldn't it just be a matter of opening the file in append mode?It would, but unfortunately CSV doesn't support 'a'
or 'a+', viz, lib/ruby/1.8/csv.rb,83 def CSV.open(path, mode, fs = nil, rs = nil, &block)
84 if mode == 'r' or mode == 'rb'
85 open_reader(path, mode, fs, rs, &block)
86 elsif mode == 'w' or mode == 'wb'
87 open_writer(path, mode, fs, rs, &block)
88 else
89 raise ArgumentError.new("'mode' must be 'r', 'rb', 'w', or 'wb'")
90 end
91 endLater,
--
Bil
http://fun3d.larc.nasa.gov
James Gray wrote:
it seems CSV only supports 'r','rb','w','wb' for open.
FasterCSV delegates to an IO object and supports all IO's modes.
So it would be the winnerInterestingly, this design choice in FasterCSV has been questioned in
the past. I just keep liking it more and more though as issues like
this arise.James Edward Gray II
It does seem a bit odd that CSV limits the modes.
On the other hand, the desired result can be achieved by creating a
new file, copy existing data, add the new data, delete (or rename to be
safe)
the original and rename the new file to the old file name.
I think supporting the append mode is easier all round...
cheers
Chris
I realize that I am jumping late into this thread. I do not understand
why the responses to "How to append to a csv file" are so complex. Why
do you need a csv module to create, edit, and/or add records to a csv
file.
As a newbie, I have written Ruby scripts that created csv file and
appended records to existing csv files without having the need for a
csv module. To append a record, I simply open the file in 'a' mode
(have not needed the a+ mode yet), write the record to the file and
then close file.
I apolized if I am out of term and stuck my nose in the wrong place.
Chris Hulan wrote:
James Gray wrote:
> On Jul 12, 2006, at 1:55 PM, Chris Hulan wrote:
>
>> it seems CSV only supports 'r','rb','w','wb' for open.
>> FasterCSV delegates to an IO object and supports all IO's modes.
>> So it would be the winner
>
> Interestingly, this design choice in FasterCSV has been questioned in
> the past. I just keep liking it more and more though as issues like
> this arise.
>
> James Edward Gray IIIt does seem a bit odd that CSV limits the modes.
On the other hand, the desired result can be achieved by creating a
new file, copy existing data, add the new data, delete (or rename to be
safe)
the original and rename the new file to the old file name.I think supporting the append mode is easier all round...
cheers
Chris--
Posted via http://www.ruby-forum.com/\.
I can't speak for the OP, but I am assuming that they were using the
CSV module because there might have been some complications in
processing the data source. And perhaps some of the CSV module's
methods helped streamline things so they didn't have to reinvent the
wheel.
No matter if you are using the CSV module or rolling your own way of
processing a data source file, you would have to parse through the
existing data in some block form and then append to the end of the
stream/array/whatever to accomplish what the OP was looking to do.
If you post a code snippet of your way to accomplishing this without
using the CSV module I would think that the basic concept and workflow
of the script would be similar...
bbiker wrote:
I realize that I am jumping late into this thread. I do not understand
why the responses to "How to append to a csv file" are so complex. Why
do you need a csv module to create, edit, and/or add records to a csv
file.As a newbie, I have written Ruby scripts that created csv file and
appended records to existing csv files without having the need for a
csv module. To append a record, I simply open the file in 'a' mode
(have not needed the a+ mode yet), write the record to the file and
then close file.I apolized if I am out of term and stuck my nose in the wrong place.
Chris Hulan wrote:
> James Gray wrote:
> > On Jul 12, 2006, at 1:55 PM, Chris Hulan wrote:
> >
> >> it seems CSV only supports 'r','rb','w','wb' for open.
> >> FasterCSV delegates to an IO object and supports all IO's modes.
> >> So it would be the winner
> >
> > Interestingly, this design choice in FasterCSV has been questioned in
> > the past. I just keep liking it more and more though as issues like
> > this arise.
> >
> > James Edward Gray II
>
> It does seem a bit odd that CSV limits the modes.
>
> On the other hand, the desired result can be achieved by creating a
> new file, copy existing data, add the new data, delete (or rename to be
> safe)
> the original and rename the new file to the old file name.
>
> I think supporting the append mode is easier all round...
>
> cheers
> Chris
>
> --
> Posted via http://www.ruby-forum.com/\.
gregarican wrote:
I can't speak for the OP, but I am assuming that they were using the
CSV module because there might have been some complications in
processing the data source. And perhaps some of the CSV module's
methods helped streamline things so they didn't have to reinvent the
wheel.No matter if you are using the CSV module or rolling your own way of
processing a data source file, you would have to parse through the
existing data in some block form and then append to the end of the
stream/array/whatever to accomplish what the OP was looking to do.If you post a code snippet of your way to accomplishing this without
using the CSV module I would think that the basic concept and workflow
of the script would be similar...
As I said I am a newby to Ruby but not to programming in general.
Now to me a csv file is simply a flatfile database stored in a text
file. The only specifications are that fields have a separator
(normally a comma) and the records have a separator (normally a
newline). In addition neither of these separators can appear within a
field.
So to me, I only need to read a record and write a record. Once a
record is read, how I slice or dice the record does not require a csv
module that provides unique functions to process the record. Remember a
csv record is a string, period. There are no other structural
requirements.
Now it is up to me to verify the sanity of the records and believe me
no module can be written to cover all possiblities since the records
are free-form and can have any format what so ever.
Usually, I open the csv file, read in the records into an array, close
the file and then process the records as appropriately. Should I need
to write those records back I either re-open the csv file in write mode
(which clobbers the original file) or open a newfile in write mode.
Write out each record. If I want to keep the original file as a back
up, I can rename it and give the new file the old name. If my program
generates new records that need to be added to an existing file, I open
the file in append mode and writeout the record(s).
I normally do not use csv files as a permanent database. They usually
are "pass-through" files..an external program may write it outputs in a
csv file which my program processes and/or my program may store its
outputs in a csv file for another program to use.