How to concatenate strings into one using loop?

Question

can someone help me with string concatenate problem. I read data from register. It's function utf(regAddr, length). I get table with decimal numbers, then I transform it into hex and to string in loop. I need concatenate these strings into one. there is not in Lua something like .= operator

function utf(regAddr, length)
  stringTable = {} 
  table.insert(stringTable, {mb:readregisters(regAddr-1,length)})

  for key, value in pairs(stringTable) do
    for i=1, length do
      v = value[i]
      v = lmcore.inttohex(v, 4)
      v = cnv.hextostr(v)   
      log(v)
    end  
  end
end

-- function(regAddr, length)
utf(30,20)

enter image description here

why are you inserting a table into stringTable for each item, why not table.insert(stringTable, mb:readregisters(regAddr-1,length))? — Oliver
– Oliver, Commented Feb 14, 2014 at 16:33
Hello, Im inserting a table into stringTable only once. its not in loop. I can also read this register as value1, value2, value3, ... , value20 = mb:readregisters(regAddr-1,20) but I think better is work with table and loop. I don`t want to have 20 variables. I need iterate via table and for each variable in table use lmcore.inttohex and cnv.hextostr to get ASCII string. Final text must be "Power Meter" in one variable. — user3159120
– user3159120, Commented Feb 14, 2014 at 16:43

Tom Blodget · Accepted Answer · 2014-02-15 01:14:49Z

7

There is no append operator for strings. Strings are immutable values.

The .. operator concatenates two string, producing a third string as a result:

local b = "con"
local c = "catenate"
local a = b .. c  -- "concatenate"

The table.concat function concatenates strings in a table, producing a string result:

local t = { "con", "catenate" }
local a = table.concat(t)  -- "concatenate"

local t = { "two", "words" }
local a = table.concat(t, " ") -- "two words"

The string.format function takes a format pattern with a list of compatible values, producing a string result:

local b = 2
local c = "words"
local a = string.format("%i %s", b, c)  -- "2 words"

local t = { 2, "words" }
local a = string.format("%i %s", unpack(t))  -- "2 words"

If you are accumulating a lot of strings that you eventually want to concatenate, you can use a table as a temporary data structure and concatenate when you are done accumulating:

local t = {}
for i = 1, 1000 do
    table.insert(t, tostring(i))
end
local a = table.concat(t) -- "1234...9991000"

For a very large number of strings, you can concatenate incrementally. See LTN 9: Creating Strings Piece by Piece and related discussions.

answered Feb 15, 2014 at 1:14

Tom Blodget

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1 Comment

user3159120 Over a year ago

Thanks a lot Tom, your last piece of code works well and helped me

Community · Accepted Answer · 2017-05-23 12:02:23Z

3

You should try the table.concat method.

Maybe this other question can help you:

Lua table.concat
Checkout this tutorial http://lua-users.org/wiki/TableLibraryTutorial

edited May 23, 2017 at 12:02

CommunityBot

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answered Feb 14, 2014 at 15:26

Rodrigo Gauzmanf

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1 Comment

user3159120 Over a year ago

Hi, I tried this function but for functions lmcore.inttohex and cnv.hextostr I need number no table. Some kind of append operator in loop seems to be solution, but I!m not sure how to do it

user3159120 · Accepted Answer · 2014-02-15 14:23:08Z

0

this code works:

function utf(regAddr, length)
    stringTable = {}
    table.insert(stringTable, {mb:readregisters(regAddr-1,length)})

    for key, value in pairs(stringTable) do
        t = {}

        for i=1, length do
            v = value[i]
            v = lmcore.inttohex(v, 4)
            v = cnv.hextostr(v)

            table.insert(t, v)
        end
        a = table.concat(t)

    end

end

-- function(regAddr, length)
utf(30,20)

answered Feb 15, 2014 at 14:23

user3159120

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