Ultisnips dynamic tabstop generation with custom justified option

Question

It seems possible to have ultisnips produce a dynamically sized array as specified here:

https://github.com/SirVer/ultisnips/blob/master/doc/examples/tabstop-generation/README.md

The array environment created however comes prespecified with left alignment on each of the columns as indicated in the example here. The snippet code that produces this is:

post_jump "create_matrix_placeholders(snip)"
snippet 'arr(\d+),(\d+)' "LaTeX array" br
\begin{array}{`!p
orient = ""
for _ in range(0, int(match.group(1))): orient += "l"
snip.rv = orient`}
`!p
snip.rv = create_matrix(match.group(1), match.group(2), "&", "\t", "\\\\\\\\\n")
`$0
\end{array}
endsnippet

Is it possible to modify this snippet so that we only have \begin{array}{|} where | is the first placeholder stop $1 so that the user can specify whether one needs left or c enter or right alignment for each column?

Answer 1

Yes, this can be done by

1. adding a $1 placeholder at \begin{array}{|}, and
2. starting the placeholders within the matrix/array from 2 and up.

The first can be done by modifying lines 3-6 with

\begin{array}{${1:`!p
orient = ""
for _ in range(0, int(match.group(1))): orient += "l"
snip.rv = orient`}}

and the second can be done by modifying the code for create_matrix() to take in an additional argument controlling the starting placeholder:

global !p
def create_matrix_placeholders(snip):
    # not shown

def create_matrix(cols, rows, sep, start, end, placeholder=1):
    res = ""
    # 
    for _ in range(0, int(rows)):
        res += start + f"${placeholder} "
        placeholder += 1
        for _ in range(0, int(cols) - 1):
            res += sep + f" ${placeholder} "
            placeholder += 1
        res += end
    return res[:-1]
endglobal

and modifying line 8 of the snippet given in the question with

snip.rv = create_matrix(match.group(1), match.group(2), "&", "\t", "\\\\\\\\\n", 2)