How to transpose the contents of lines and columns in a file in Vim?

Here is a command in Vim language. So you don't have to compile Vim with +python support.

function! s:transpose()
    let maxcol = 0
    let lines = getline(1, line('$'))

    for line in lines
        let len = len(line)
        if len > maxcol 
            let maxcol = len
        endif
    endfor

    let newlines = []
    for col in range(0, maxcol - 1)
        let newline = ''
        for line in lines
            let line_with_extra_spaces = printf('%-'.maxcol.'s', line)
            let newline .= line_with_extra_spaces[col]
        endfor
        call add(newlines, newline)
    endfor

    1,$"_d
    call setline(1, newlines)
endfunction

command! TransposeBuffer call s:transpose()

Put this in newly created .vim file inside vim/plugin dir or put this to your [._]vimrc.
Execute :TransposeBuffer to transpose current buffer

Vim support for a number of scripting languages built in -- see the Python interface as an example.

Just modify vim.current.buffer appropriately and you're set.

To be a little more specific:

function! Rotate()
python <<EOF
import vim, itertools
max_len = max((len(n) for n in vim.current.buffer))

vim.current.buffer[:] = [
    ''.join(n) for n in itertools.izip(
        *( n + ' ' * (max_len - len(n))
           for n in vim.current.buffer))]
EOF
endfunction