The consensus is that it is a very bad idea for a file nominally described as a CSV file to have a varying numbers of fields from record to record. If you have need for such a file and go to whatever lengths you need to in order to create it, please mark it as something other than a CSV file when you are done.
With this in mind, you may be in a better position to understand why the pre-built facilities do not provide much support in your endeavor.
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Mehmet Suzen <msuzen@mango-solutions.com> wrote:


This might be obvious but I was wondering if anyone knows quick and easy
way of writing out a CSV file with varying row lengths, ideally an
initial data read from a CSV file which has the same format. See example
below.


I found it quite strange that R cannot write it in one go, so one must
append blocks or post-process the file, is this true? (even Ruby can do
it!!) 

Otherwise it puts ,"","" or similar for missing column values in the
shorter length rows and fill=FALSE option do not work!

I don't want to post-process if possible.

See this post:
http://r.789695.n4.nabble.com/Re-read-csv-trap-td3301924.html

Example that generated Error!

writeLines(c("A,B,C,D",
"1,a,b,c",
"2,f,g,c",
"3,a,i,j",
"4,a,b,c",
"5,d,e,f",
"6,g,h,i,j,k,l,m,n"),
con=file("test.csv"))

read.csv("test.csv")
try(read.csv("test.csv",fill=FALSE))
LEGAL NOTICE\ This message is intended for the use o...{...{{dropped:14}}

