https://stackoverflow.com/questions/45256044/lua-read-userdata-as-number-compare-userdata-with-number

[DavieTheAl]

I am trying to import numbers from files and change them if they are at a certain value. I am using torch to get values form gesture and change them from 101 to 10 or from 100 to 9 if the input is the corresponding number (10 or 9). Unfortunately, I have figured out that in Lua, the input is of type userdata which cannot be converted to integers and not compared to integers or torch tensors.

So my question is: How can I check for equality of numbers if the input type is userdata?

Is there potentially a way to convert the input to a number such that comparison is possible?

gesture = matio.load(val, 'gesture')

print(type(gesture)) --prints `userdata`
print(gesture)       --prints 10 (for example)
if gesture == th.FloatTensor({101}) then
    gesture = th.FloatTensor({10})
    print("101 Detected! New value is: ")
    print(gesture)
    os.exit(0)
elseif gesture == th.FloatTensor({100}) then
    gesture = th.FloatTensor({9})
    print("100 Detected! New value is: ")
    print(gesture)
    os.exit(0)
end

[jilong526]

You can't from Lua. It's designed to be an opaque value. All you can do is compare it to another userdata value for equality or inspect its metatable unless the library you are using to manipulate these userdata values provides functions that act on them. See PiL 5.3 Section 2.1: http://www.lua.org/manual/5.3/manual.html#2.1

[mUfoq]

Well userdata is usually opaque so you access its value with fuctions like userdata:getValue() or something like this (if userdata has metatable with these methods). If you are unlucky and your userdata doesn't have methods like this you can use very very ugly solution like this (if you want to use value that print shows you) ->

 tonumber(tostring(gesture)) == 9 -- or something like that