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


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
orient = ""
for _ in range(0, int(match.group(1))): orient += "l"
snip.rv = orient`}
snip.rv = create_matrix(match.group(1), match.group(2), "&", "\t", "\\\\\\\\\n")

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?

1 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

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]

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)
  • Thank you. I tried carefully replicating your code. However, it does not seem to work. Specifically, when I type genarr3x4, there is a bunch of l's that get placed on top of the expanded snippet. Example can be seen imgur.com/a/dDag2KO
    – Tryer
    Nov 23, 2022 at 17:04
  • Here is the diff of the after (lhs) vs before (rhs) imgur.com/55xnvnK imgur.com/gTKm1NG to ensure I have implemented your suggestions exactly.
    – Tryer
    Nov 23, 2022 at 17:14
  • 1
    I got the same result that you did. It looks like the problem is with the implementation of the expansion of anonymous snippets.. Let me see if there is a workaround
    – husB
    Nov 24, 2022 at 4:10
  • Well thank you. I certainly appreciate the time and effort.
    – Tryer
    Nov 24, 2022 at 4:18
  • Unfortunately I could not find a workaround.. The details did not work, but I'll leave the main idea here: Currently the snippet is supposed to expand as genarr3x4 -> \begin{array}{${1:lll}} { ... placeholders to be anonymously expanded ... } \end{array} -> \begin{array}{${1:lll}} { $2 & $3 ... } \end{array}. This "double expansion" seems to mess up Ultisnips. Instead, empty the snippet before any anonymous expansion, ie. genarr3x4 -> (get the value of nrow, ncol, and clear that current line) -> { anonymously expand into \begin{array} ${1:lll} $2 & $3 ... } all at once
    – husB
    Nov 24, 2022 at 4:40

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