This question already has answers here:
Search for an item in a Lua list
(12 answers)
Lua find a key from a value
(3 answers)
Closed 9 years ago.
I have this table:
maps = {4707191, 4747722, 1702169, 3994471, 4708958, 4008546, 4323335, 4516043, 4612295, 3469987, 4337892, 238378, 3088188, 329627, 3526384, 433483}
How can I make a script so if 1702169 (for example) is picked from the table, it prints ''That's the number''?
The easiest way to do what (i think) you want is with pairs() function. This is a stateless iterator which you can read more about here: http://www.lua.org/pil/7.3.html
If you simply want to scan through the entire table and see if it contains a value, then you can use this simple code:
local maps = {4707191, 4747722, 1702169, 3994471, 4708958, 4008546, 4323335, 4516043, 4612295, 3469987, 4337892, 238378, 3088188, 329627, 3526384, 433483}
local picked = 1702169
for i, v in pairs(maps) do
if v == picked then
print("That's the number")
break
end
end
The above code will iterate through the whole table where i is the key and v is the value of the table[key]=value pairs.
I am slightly unclear about your end goal, but you could create this into a function and/or modify it to your actual needs. Feel free to update your original post with more information and I can provide you with a more specific answer.
Related
This question already has answers here:
Null-aware operator with Maps
(7 answers)
Closed 3 years ago.
How do you check for nulls when accessing second level map elements?
E.g.
var clientName = item['client']['name'];
will throw an exception if item does not contain client
I'd like something like
item['client']?['name']
or
item['client']?.['name']
But that won't compile.
Surely I can do item['client'] twice or introduce a local var for it but that feels subpar.
I think that this is similar to a question I asked some time ago.
Basically, this would be the solution for your case:
(item['client'] ?? const {})['name']
This makes use of the null-aware ?? operator which just returns an empty map in the case that 'client' is not present in item.
With putIfAbsent, you can use ? operator.
item.putIfAbsent("client", (){})
?.putIfAbsent("name", (){});
https://api.dartlang.org/stable/2.3.1/dart-core/Map/putIfAbsent.html
This question already has answers here:
Concatenation of tables in Lua
(13 answers)
Closed 7 years ago.
Is there an easy way to concatenate two tables which are sequences? For example
a = {1, 2, 3}
b = {5, 6, 7}
c = cat(a,b)
where c would be the table {1,2,3,5,6,7}?
function cat(t, ...)
local new = {unpack(t)}
for i,v in ipairs({...}) do
for ii,vv in ipairs(v) do
new[#new+1] = vv
end
end
return new
end
It uses iteration to add the elements of each array to a new one.
It's also worth noting that {unpack(t)} will only work if you have less than a specific number of elements, due to how tuples work in Lua. This varies across versions and depending on what you're doing, but if it's small you probably have nothing to worry about.
This question already has answers here:
Lua for loop reduce i? Weird behavior [duplicate]
(3 answers)
Closed 7 years ago.
im trying this in lua:
for i = 1, 10,1 do
print(i)
i = i+2
end
I would expect the following output:
1,4,7,10
However, it seems like i is getting not affected, so it gives me:
1,2,3,4,5,6,7,8,9,10
Can someone tell my a bit about the background concept and what is the right way to modify the counter variable?
As Colonel Thirty Two said, there is no way to modify a loop variable in Lua. Or rather more to the point, the loop counter in Lua is hidden from you. The variable i in your case is merely a copy of the counter's current value. So changing it does nothing; it will be overwritten by the actual hidden counter every time the loop cycles.
When you write a for loop in Lua, it always means exactly what it says. This is good, since it makes it abundantly clear when you're doing looping over a fixed sequence (whether a count or a set of data) and when you're doing something more complicated.
for is for fixed loops; if you want dynamic looping, you must use a while loop. That way, the reader of the code is aware that looping is not fixed; that it's under your control.
When using a Numeric for loop, you can change the increment by the third value, in your example you set it to 1.
To see what I mean:
for i = 1,10,3 do
print(i)
end
However this isn't always a practical solution, because often times you'll only want to modify the loop variable under specific conditions. When you wish to do this, you can use a while loop (or if you want your code to run at least once, a repeat loop):
local i = 1
while i < 10 do
print(i)
i = i + 1
end
Using a while loop you have full control over the condition, and any variables (be they global or upvalues).
All answers / comments so far only suggested while loops; here's two more ways of working around this problem:
If you always have the same step size, which just isn't 1, you can explicitly give the step size as in for i =start,end,stepdo … end, e.g. for i = 1, 10, 3 do … or for i = 10, 1, -1 do …. If you need varying step sizes, that won't work.
A "problem" with while-loops is that you always have to manually increment your counter and forgetting this in a sub-branch easily leads to infinite loops. I've seen the following pattern a few times:
local diff = 0
for i = 1, n do
i = i+diff
if i > n then break end
-- code here
-- and to change i for the next round, do something like
if some_condition then
diff = diff + 1 -- skip 1 forward
end
end
This way, you cannot forget incrementing i, and you still have the adjusted i available in your code. The deltas are also kept in a separate variable, so scanning this for bugs is relatively easy. (i autoincrements so must work, any assignment to i below the loop body's first line is an error, check whether you are/n't assigning diff, check branches, …)
This question already has answers here:
What does ||= (or-equals) mean in Ruby?
(23 answers)
Closed 8 years ago.
In my readings about structuring methods with options hashes for ruby, I've run into a coding "motif" a few times that I can't explain. Since I don't know what it's called, I'm having a lot of difficulty looking it up to learn more about it.
Here's an example:
1 def example_method(input1, options={})
2
3 default_options = {
4 :otherwise => "blue",
5 :be_nil => nil
6 }
7
8 options[:be_nil] ||= options[:otherwise]
9
10 # other code goes down here
11 end
So above, on line 8, you can see what I'm talking about. From what I can put together, the line of code acts similarly to a tertiary operator. Under one condition, it sets a variable to one value... under a different condition, it sets the variable to a different value. In this case, however, the code updates a hash that's stored in the "options" variable. Is that a correct assumption? Furthermore, what is this style/operator/functionality called?
THis is a conditional assignment. The variable on the left will be assigned a value if it is nil or false. This is the short for of saying:
unless options[:be_nil]
options[:be_nil] = options[:otherwise]
end
I asked a question similar to this the other day, but another bug popped up "attempt to concatenate table and string"
local questions={
EN={
Q2={"Who is the lead developer of Transformice?","Tigrounette"},
Q4={"What is Eminem's most viewed song on youtube?","I love the way you lie"},
Q6={"What is the cubic root of 27?","3"},
Q8={"What are the first 3 digits of Pi","3.141"},
Q10={"What is the most populated country?","China"},
Q12={"What is the plural of the word 'Person'?","People"},
Q14={"Entomology is the science that studies ...?","Insects"},
Q16={"Who was the creator of the (bot ran) minigame fight?","Cptp"},
Q18={"The ozone layer restricts ... radiation","Ultraviolet"},
Q20={"Filaria is caused by ...","Mosquitos"}
}
local main = questions.EN["Q"..math.random(1,20)].."%s" -- bug here
local current_answer_en = string.gsub(current_question_en,1,2)
What type of object is questions.EN["Q"..math.random(1,20)]? Say random is 15, what type of object is questions.EN["Q6"]? It is a {"What is the cubic root of 27?","3"}, which is a table, which Lua doesn't know how to concatenate with a string ("%s" in your case). If you want to concatenate with the first item of this table, then
local main = questions.EN["Q"..math.random(1,20)][1] .. "%s"
Note however that you will need the "random with step" function that I posted in math.random function with step option?, otherwise you could get that the table EN["Q"..something] is nil (if the random number is an odd number, in the code you posted).
Note sure what you are trying to do with current_question_en but if you are trying to extract the question and answer you could do something like this:
local QA = questions.EN["Q"..math.random(1,20)] -- this is a table
local question, answer = QA[1], QA[2]
The other option is that you build your table like this:
local questions={
EN={
Q2={q="Who is ..?", a="Tigrounette"},
Q4={q="What is ...?", a="I love the way you lie"},
...
}
}
Then you could use
local QA = questions.EN["Q"..math.random(1,20)] -- this is a table
print("The question:", QA.q)
print("The answer:", QA.a)
Not sure what you're trying to do with string.gsub but it does not take integers as 2nd and 3rd args.