Problem 57829. Convert vector of strings to lower triangular matrix

Christian Schröder

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Given a non-empty vector vec of strings, please put its elements into the lower triangular half of a square matrix M column-wise. The remaining elements of M, those not filled this way, should contain empty strings, "".
For example, given
seq = [ "a" "b" "c" ]
your code should return
M = [ 
    "a" "" 
    "b" "c"
]
while for
seq = strsplit("I like wine, and I like cheese, I like the smell of a westerly breeze.")
it should return
M = [
    "I"        ""           ""           ""            ""     
    "like"     "like"       ""           ""            ""     
    "wine,"    "cheese,"    "the"        ""            ""     
    "and"      "I"          "smell"      "a"           ""     
    "I"        "like"       "of"         "westerly"    "breeze."
]
The number of elements of vec is not restricted (other than being positive), BTW, so e.g.
seq = [ "a" "b" "c" "d" ]
should yield
M = [ 
    "a" ""  "" 
    "b" "d" ""
    "c" ""  ""
]
Related: Problem 44457. Triangle of numbers.
P.S. the test suite will not check for cheating, but please be a good sport.