[R] Changing a value in a particular row and column within a text file

[T.V. Nguyen]

On 17 Dec 2010, at 01:13, Mauricio Zambrano wrote:

> Dear list,
> 
> I need to change a value within a particular line of a plain text file
> with characters and numbers, and I haven't found any way of doing this
> by using R.
> 
> What I have a is a file that doesn't have tabular data (so, I think
> that 'read.table' or 'read.delim' are not the right tools for this),
> but some text, and I now exactly the row that has to be modified and
> the columns within that row that have to be changed with a new
> numerical value.
> 
> I don't' know any way of reading a text file line by line in R, and
> this is the only solution in R that I have figured out so far...
> 
> Any idea about how can I do this ?.

readLines will read lines from a flat file and create a character array:

> list <- readLines("twelvedaysofchristmas.txt")
> head(list)
[1] "12 Drummers Drumming" "11 Pipers Piping"    
[3] "10 Lords-a-Leaping"   "9 Ladies Dancing"    
[5] "8 Maids-a-Milking"    "7 Swans-a-Swimming" 

You can either edit the line you want manually, or use sub to make changes:

> sub("Lords-a-Leaping","Jaffa Cakes",list)
> head(list)
[1] "12 Drummers Drumming" "11 Pipers Piping"    
[3] "10 Jaffa Cakes"       "9 Ladies Dancing"    
[5] "8 Maids-a-Milking"    "7 Swans-a-Swimming"  

writeLines will write it back:

> writeLines(list,"twelvedaysofchristmas.txt")

Hope this helps, --t

> 
> 
> Thanks in advance for any help,
> 
> Mauricio
> 
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--
Thomson Van Nguyen
Centre for Mathematical Studies
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