Question

I want to use stack to a data frame and keep duplicate columnnames from a original data frame.

a1<-data.frame(1:10,11:20,21:30)
colnames(a1)<-c('a','b','a')
a2<-stack(a1)

Above adds ‘a.1’ for duplicate column names for ‘a’ in a2. I want to keep it as ‘a’. Is there any option for this in stack?

Alternatively I tried to replace all ‘a1.1’ using a loop. I wasn’t successful in the large table with many duplicate names. Is there any better example for replacing the pattern (strings) in r rows?

Finally, I am here asking my first question in forum. Thanks for your help.

Answer 1

By looking at the code for stack by:

> getS3method('stack', 'default')

function (x, ...) 
{
    x <- as.list(x)
    keep <- unlist(lapply(x, is.vector))
    if (!sum(keep)) 
        stop("at least one vector element is required")
    if (!all(keep)) 
        warning("non-vector elements will be ignored")
    x <- x[keep]
    data.frame(values = unlist(unname(x)), ind = factor(rep.int(names(x), 
        lapply(x, length))), stringsAsFactors = FALSE)
}

As you see the ... parameter is not passed to the data.frame creation. You could modify this function by creating say stack2 as follows:

stack2 <- function (x, ...) 
{
    x <- as.list(x)
    keep <- unlist(lapply(x, is.vector))
    if (!sum(keep)) 
        stop("at least one vector element is required")
    if (!all(keep)) 
        warning("non-vector elements will be ignored")
    x <- x[keep]
    data.frame(values = unlist(unname(x)), ind = factor(rep.int(names(x), 
        lapply(x, length))), stringsAsFactors = FALSE, ...) # note the ... here
}
# after copy/paste of stack2 function
> stack2(a1, check.names = FALSE)
   values ind
1       1   a
2       2   a
3       3   a
4       4   a
5       5   a
6       6   a
7       7   a
8       8   a
9       9   a
10     10   a
11     11   b
12     12   b
13     13   b
14     14   b
15     15   b
16     16   b
17     17   b
18     18   b
19     19   b
20     20   b
21     21   a
22     22   a
23     23   a
24     24   a
25     25   a
26     26   a
27     27   a
28     28   a
29     29   a
30     30   a

Note: Don’t pass stringsAsFactors = . argument to this stack2 function as its already passed. Probably that’s why they don’t pass the ... argument?