How to reshape tabular data to one row per group

Question

I am an R (and coding novice) and I am looking for a way to reconfigure Table A show below into Table B.

Table A:

type   x1  x2  x3  
A      4   6            


        

Answer 1

To me, this solution seems pretty straightforward

# split the data frame by type and use unlist, which will provide names
ld <- lapply(split(d[-1], d[["type"]]), unlist)

# gather all the unique names in the list
ldNames <- Reduce(unique, lapply(ld, names))

# use the names to index each list element, which makes them
# all of equal length and suitable for row binding.  
do.call(rbind, lapply(ld, function(x) x[ldNames]))
#   x11 x12 x13 x21 x22 x23 x31 x32 x33
# A   4   7   9   6   4   6   9   1   2
# B   1   2  NA   3   7  NA   8   9  NA

If the order of the output above is not satisfactory, you can rearrange:

# save the output from above
d2 <- do.call(rbind, lapply(ld, function(x) x[ldNames]))
# reorder the names
ldNames_sorted <- c(matrix(ldNames, ncol = (ncol(d) - 1), byrow = TRUE))

# apply the new order.
d2 <- d2[, ldNames_sorted]
#  x11 x21 x31 x12 x22 x32 x13 x23 x33
#A   4   6   9   7   4   1   9   6   2
#B   1   3   8   2   7   9  NA  NA  NA

To add a column for type instead of using row names, one method would be:

data.frame(type = row.names(d2), d2)