CODEWITHSUNDEEP
arrayslua
Nick Ramsbottom
Nick Ramsbottom

Reputation: 673

Select which array to write to based on variables given to a function, Lua

I am trying to run this code:

function calcs.grps(Number,ion_color)
    grp .. ion_color .. Y[Number] = (ion_py_mm)
    grp .. ion_color .. Z[Number] = (ion_pz_mm)
end

in a Lua script, the arrays already exist (eg grp2Y,grp5Z etc) and I want to use this function to populate them based upon the two variables fed in. I keep getting the error ' '=' expected near '..' '. What am I doing wrong?

To flesh it out a bit:

I am 'flying' 120 ions in my simulation. This is actually 12 groups of 10 ions. The individual groups of 10 are distinguished by ion_color, which is an integer value from 1 to 12. The variable 'Number' just cycles through 1 to 10 each time before moving on to the next color. Once I have populated these arrays I want to get the standard deviation for each group.

Thank you!

Upvotes: 1

Views: 62

Answers (2)

warspyking
warspyking

Reputation: 3113

The technical answer to your question is to simply index _G, _G is a table which holds all global variables:

function calcs.grps(Number,ion_color)
    _G['grp' .. ion_color .. Y'][Number] = (ion_py_mm)
    _G['grp' .. ion_color .. 'Z'][Number] = (ion_pz_mm)
end

But I think the better question, is why aren't you organizing it like this...

local ions = {
    Red = {
        {
            Y = 0, --Y property
            Z = 0 --Z property
        },
        --Continue your red ions
    },
    NewColor = {
            Y = 0, --Y property
            Z = 0 --Z property
        },
        --Continue this color's ions
    },
    --You get the idea
}

function calcs.grps(color, number)
    ions[color][number].Y = (ion_py_mm)
    ions[color][number].Z = (ion_pz_mm)
end

Then you would pass a color, and a number indicating which ion of this color

It looks a lot cleaner, IMO.

Upvotes: 1

Oleg V. Volkov
Oleg V. Volkov

Reputation: 22431

You can't "construct" name of variable, but you can construct an index. Use two levels of nested tables.

function calcs.grps(Number,ion_color)
    ion['grp' .. ion_color .. 'Y'][Number] = (ion_py_mm)
    ion['grp' .. ion_color .. 'Z'][Number] = (ion_pz_mm)
end

Well, actually you can, since all global variables are just entries in _G table, but don't do that since it is bad - it is unreadable, makes stuff spill to other functions you didn't intend to, etc.

Upvotes: 3

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