LUA: Simpler string pattern solution

Question

I'm studying LUA on my own and would like a little help on this next piece of code:

offset= "1h2m3s4f"

off_h = offset:match("(%d+)h")
off_m = offset:match("(%d+)m")
off_s = offset:match("(%d+)s")
off_f = offset:match("(%d+)f")

print(off_h)
print(off_m)
print(off_s)
print(off_f)

I've tried everything to concat the pattern into a single line offset:match but after reading many ressources online I am still clueless how to do it. The problem is, the user might enter only 2m3s4f without any numbers for h or he might enter only 1m2f.

My tests on a single pattern check were resulting in full nil values when I removed one of the pattern condition. I tried adding the magic char ? to the different patterns but that didn't do the trick. Any pointer would be appreciated! Thanks,

See also stackoverflow.com/a/48522847/107090

lhf
– lhf

2018-02-17 00:16:14 +00:00
Commented Feb 17, 2018 at 0:16 — lhf
– lhf, Commented Feb 17, 2018 at 0:16

Egor Skriptunoff · Accepted Answer · 2018-02-17 12:52:25Z

2

for _, offset in ipairs{"1h2m3s4f", "2m3s4f", "1m2f"} do
   local fields = {}
   offset:gsub("(%d+)([hmsf])", function(n,u) fields[u] = n end)
   print(fields.h, fields.m, fields.s, fields.f)
end

Output:

1    2    3    4
nil  2    3    4
nil  1    nil  2

-- Shortest, but slowest variant
for _, offset in ipairs{"1h2m3s4f", "2m3s4f", "1m2f"} do
   local h, m, s, f = offset:match"^(%d-)h?(%d-)m?(%d-)s?(%d-)f?$"
   print(h, m, s, f)
end

Output:

1  2  3  4
   2  3  4
   1     2

edited Feb 17, 2018 at 12:52

answered Feb 16, 2018 at 23:50

Egor Skriptunoff

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4 Comments

hjpotter92 Over a year ago

Any reason for doing the reverse in first approach? I mean is it faster?

hjpotter92 Over a year ago

Yes, I understand that. My question was, how is that any different from "^(%d-)h?(%d-)m?(%d-)s?(%d-)f?$" pattern match? And since there are no reverse involved; wouldn't it be faster?

Egor Skriptunoff Over a year ago

@hjpotter92 - Yes, reverse()-version is not any better than the last variant. Removed it.

LumiJay Over a year ago

Huge thanks guys! I'll study both answers posted to increase my LUA knowledge. Thanks a bunch for the answers!!

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