I have to be honest that I don't quite understand Lua that well yet. I am trying to overwrite a local numeric value assigned to a set table address (is this the right term?).
The addresses are of the type:
project.models.stor1.inputs.T_in.default, project.models.stor2.inputs.T_in.default and so on with the stor number increasing.
I would like to do this in a for loop but cannot find the right expression to make the entire string be accepted by Lua as a table address (again, I hope this is the right term).
So far, I tried the following to concatenate the strings but without success in calling and then overwriting the value:
for k = 1,10,1 do
project.models.["stor"..k].inputs.T_in.default = 25
end
for k = 1,10,1 do
"project.models.stor"..j..".T_in.default" = 25
end
EDIT:
I think I found the solution as per https://www.lua.org/pil/2.5.html:
A common mistake for beginners is to confuse a.x with a[x]. The first form represents a["x"], that is, a table indexed by the string "x". The second form is a table indexed by the value of the variable x. See the difference:
for k = 1,10,1 do
project["models"]["stor"..k]["inputs"]["T_in"]["default"] = 25
end
You were almost close.
Lua supports this representation by providing a.name as syntactic sugar for a["name"].
Read more: https://www.lua.org/pil/2.5.html
You can use only one syntax in time.
Either tbl.key or tbl["key"].
The limitation of . is that you can only use constant strings in it (which are also valid variable names).
In square brackets [] you can evaluate runtime expressions.
Correct way to do it:
project.models["stor"..k].inputs.T_in.default = 25
The . in models.["stor"..k] is unnecessary and causes an error. The correct syntax is just models["stor"..k].
In order to extract the values (records) of an orddict as a sorted list, tried this:
-module(test).
-compile(export_all).
-record(node, {name="", cost=0}).
test() ->
List = orddict:append("A",#node{name="A",cost=1},
orddict:append("B",#node{name="B",cost=2},
orddict:new())),
lists:sort(fun({_,A},{_,B}) -> A#node.cost =< B#node.cost end,
orddict:to_list(List)).
The sort fails with exception error: {badrecord,node}.
What would be the correct syntax?
Solved:
The correct insertion method is orddict:store/2 instead of orddict:append/2. Then the pattern {_,A} matches for the comparison function.
The correct syntax is:
lists:sort(fun({_,[A]},{_,[B]}) -> A#node.cost =< B#node.cost end,
orddict:to_list(List)).
I not found note about this in documentation,but you can look in source code of module.
As #Pascal write in comments the reason is that orddict:append/3 is a function provided to append a value to an existing Key/Value pair where Value must be a list. In the use case, the key doesn't exist, so the pair is created and the Value append to an empty list.
Btw, you always can print and compare real and expected result.
io:format("~p~n",[orddict:to_list(List)])
For your example that is:
[{"A",[{node,"A",1}]},{"B",[{node,"B",2}]}]
I'm trying to to get a list of three items with their relevant information based on a collection of information:
product(I):-
I = [_,_,_,_], %Type,Brand,Category,Value
cheaper(item(apple,_,_),item(_,kay,_,_),I),
cheaper(item(bar,_,_,_),item(_,_,fruit,_),I),
member(item(_,kay,_,2),I),
member(item(apple,granny,_,_),I),
member(item(bar,_,chocolate,_),I),
/* Below not given */
member(item(cracker,_,_,_),I),
member(item(_,_,biscuit,_),I),
member(item(_,_,_,4),I),
member(item(_,_,_,5),I).
cheaper(X,Y,H) :- %Used to determine the item values
item(X,_,_,A),
item(Y,_,_,B),
A<B.
When I try running it I encounter an error:
?- product(I).
ERROR: cheaper/3: Undefined procedure: item/4
Exception: (8) item(item(apple, _G3604, _G3605), _G3651, _G3652, _G3653) ?
I understand that item isn't a procedure, however what can I used for checking the value for apple against the value for bar?
First, the obvious note, you're calling cheaper wrong once:
cheaper(item(apple,_,_),item(_,kay,_,_),I),
↑
Only three values, not four.
If item isn't a procedure, you mustn't call it, but use destructuring.
Also you want those items you're checking with cheaper to be part of the list, right? If so, you'll have to check that. And you can use unification to extract the values that you need:
cheaper(X,Y,I) :-
member(X,I),
member(Y,I),
[item(_,_,_,A),item(_,_,_,B)] = [X,Y],
A<B.
Now you'll get some errors regarding not instantiated argument. That's because you are checking not (yet) set variables if they are greater than each other. To avoid this, move the cheaper/3 calls to the end of your clause body:
product(I):-
I = [_,_,_,_], %Type,Brand,Category,Value
member(item(_,kay,_,2),I),
member(item(_,_,_,4),I),
member(item(_,_,_,5),I),
member(item(apple,granny,_,_),I),
member(item(bar,_,chocolate,_),I),
/* Below not given */
member(item(cracker,_,_,_),I),
member(item(_,_,biscuit,_),I),
cheaper(item(apple,_,_,_),item(_,kay,_,_),I), % note the 4th argument
cheaper(item(bar,_,_,_),item(_,_,fruit,_),I).
With this, you'll get one solution and then it fails with an error. This is, because you only give three values for the price slot and you have four items and prolog will check A > 2.
Sorry, in my other answer I didn't look for what the poster was trying to achieve and I think that this is better than a complete reedit. (glorious SO mods let me know if I'm wrong)
Is there any way that
PadRight[a \[PlusMinus] b,2,""]
Returns
{a \[PlusMinus] b,""}
Instead of
a \[PlusMinus] b \[PlusMinus] ""
?
I believe that i need to somehow deactivate the operator properties of [PlusMinus].
Why do i need this?
I'm creating a program to display tables with physical quantities. To me, that means tables with entries like
(value of a) [PlusMinus] (uncertainty of a)
When i have several columns with different heights, i'm stuffing the shorter ones with "", so i can use Transpose the numeric part of the table.
If the column has more than one entrie, there's no problem:
PadRight[{a \[PlusMinus] b,c \[PlusMinus] d},4,""]
gives what i want:
{a \[PlusMinus] b,c \[PlusMinus] d,"",""}
It is when the column has only one entrie that my problem appears.
This is the code that constructs the body stuffed with "":
If[tested[Sbody],1,
body = PadRight[body, {Length[a], Max[Map[Length, body]]
With
tested[a__] :=
If[Length[DeleteDuplicates[Map[Dimensions, {a}]]] != 1, False,
True];
, a function that discovers if is arguments have the same dimension
and
a={Quantity1,Quantity2,...}
Where the quantities are the one's that i want on my table.
Thanks
First you need to be aware of that any expression in Mathematica is in the form of Head[Body]
where body may be empty, a single expression or a sequence of expressions separated by commas
Length operate on expressions, not necessarily lists
so
Length[PlusMinus[a,b]]
returns 2 since the body of the expression contains to expressions (atoms in this case) that are a and b
Read the documentation on PadRight. The second argument define the final length of the expression
so
PadRight[{a,b},4,c] results with a list of length 4 with the last two elements equal to
PadRight[{a,b},2,c] results with the original list since it is already of length 2
Therefore
PadRight[PlusMinus[a,b],2,anything] just returns the same PlusMinus[a,b] unchanged since it is already of length 2
so, youר first example is wrong. You are not able to get a result with head List using PadRight when you try to pad to an expression with head PlusMinus
There is no problem of executing
PadRight[PlusMinus[a,b],3,""]
but the result looks funny (at best) and logically meaningless, but if this is what you wanted in the first place you get it, and following my explanations above you can figure out why
HTH
best
yehuda