Say I have this dictionary in Lua
places = {dest1 = 10, dest2 = 20, dest3 = 30}
In my program I check if the dictionary has met my size limit in this case 3, how do I push the oldest key/value pair out of the dictionary and add a new one?
places["newdest"] = 50
--places should now look like this, dest3 pushed off and newdest added and dictionary has kept its size
places = {newdest = 50, dest1 = 10, dest2 = 20}
It's not too difficult to do this, if you really needed it, and it's easily reusable as well.
local function ld_next(t, i) -- This is an ordered iterator, oldest first.
if i <= #t then
return i + 1, t[i], t[t[i]]
end
end
local limited_dict = {__newindex = function(t,k,v)
if #t == t[0] then -- Pop the last entry.
t[table.remove(t, 1)] = nil
end
table.insert(t, k)
rawset(t, k, v)
end, __pairs = function(t)
return ld_next, t, 1
end}
local t = setmetatable({[0] = 3}, limited_dict)
t['dest1'] = 10
t['dest2'] = 20
t['dest3'] = 30
t['dest4'] = 50
for i, k, v in pairs(t) do print(k, v) end
dest2 20
dest3 30
dest4 50
The order is stored in the numeric indices, with the 0th index indicating the limit of unique keys that the table can have.
Given that dictionary keys do not save their entered position, I wrote something that should be able to help you accomplish what you want, regardless.
function push_old(t, k, v)
local z = fifo[1]
t[z] = nil
t[k] = v
table.insert(fifo, k)
table.remove(fifo, 1)
end
You would need to create the fifo table first, based on the order you entered the keys (for instance, fifo = {"dest3", "dest2", "dest1"}, based on your post, from first entered to last entered), then use:
push_old(places, "newdest", 50)
and the function will do the work. Happy holidays!
Related
In the Help Documentation of Scilab 6.0.2, I can read the following instruction on the Overloading entry, regarding the last operation code "iext" showed in this entry's table:
"The 6 char code may be used for some complex insertion algorithm like x.b(2) = 33 where b field is not defined in the structure x. The insertion is automatically decomposed into temp = x.b; temp(2) = 33; x.b = temp. The 6 char code is used for the first step of this algorithm. The 6 overloading function is very similar to the e's one."
But I can't find a complete example on how to use this "char 6 code" to overload a function. I'm trying to use it, without success. Does anyone have an example on how to do this?
The code bellow creates a normal "mlist" as a example. Which needs overloading functions
A = rand(5,3)
names = ["colA" "colB" "colC"]
units = ["ft" "in" "lb"]
M = mlist(["Mlog" "names" "units" names],names,units,A(:,1),A(:,2),A(:,3))
Following are the overload functions:
//define display
function %Mlog_p(M)
n = size(M.names,"*")
formatStr = strcat(repmat("%10s ",1,n)) + "\n"
formatNum = strcat(repmat("%0.10f ",1,n)) + "\n"
mprintf(formatStr,M.names)
mprintf(formatStr,M.units)
disp([M(M.names(1)),M(M.names(2)),M(M.names(3))])
end
//define extraction operation
function [Mat]=%Mlog_e(varargin)
M = varargin($)
cols = [1:size(M.names,"*")] // This will also work
cols = cols(varargin($-1)) // when varargin($-1) = 1:1:$
Mat = []
if length(varargin)==3 then
for i = M.names(cols)
Mat = [Mat M(i)(varargin(1))]
end
else
for i=1:size(M.names(cols),"*")
Mat(i).name = M.names(cols(i))
Mat(i).unit = M.units(cols(i))
Mat(i).data = M(:,cols(i))
end
end
endfunction
//define insertion operations (a regular matrix into a Mlog matrix)
function ML=%s_i_Mlog(i,j,V,M)
names = M.names
units = M.units
A = M(:,:) // uses function above
A(i,j) = V
ML = mlist(["Mlog" "names" "units" names],names,units,A(:,1),A(:,2),A(:,3))
endfunction
//insertion operation with structures (the subject of the question)
function temp = %Mlog_6(j,M)
temp = M(j) // uses function %Mlog_e
endfunction
function M = %st_i_Mlog(j,st,M)
A = M(:,:) // uses function %Mlog_e
M.names(j) = st.name // uses function above
M.units(j) = st.unit // uses function above
A(:,j) = st.data // uses function above
names = M.names
units = M.units
M = mlist(["Mlog" "names" "units" names],names,units,A(:,1),A(:,2),A(:,3))
endfunction
The first overload (displays mlist) will show the matrix in the form of the following table:
--> M
M =
colA colB colC
ft in lb
0.4720517 0.6719395 0.5628382
0.0623731 0.1360619 0.5531093
0.0854401 0.2119744 0.0768984
0.0134564 0.4015942 0.5360758
0.3543002 0.4036219 0.0900212
The next overloads (extraction and insertion) Will allow the table to be access as a simple matrix M(i,j).
The extraction function Will also allow M to be access by column, which returns a structure, for instance:
--> M(2)
ans =
name: "colB"
unit: "in"
data: [5x1 constant]
The last two functions are the overloads mentioned in the question. They allow the column metadata to be changed in a structure form.
--> M(2).name = "length"
M =
colA length colC
ft in lb
0.4720517 0.6719395 0.5628382
0.0623731 0.1360619 0.5531093
0.0854401 0.2119744 0.0768984
0.0134564 0.4015942 0.5360758
0.3543002 0.4036219 0.0900212
I would like to iterate over a list and occasionally delete items of said list. Below a toy example:
function delete_item!(myarray, item)
deleteat!(myarray, findin(myarray, [item]))
end
n = 1000
myarray = [i for i = 1:n];
for a in myarray
if a%2 == 0
delete_item!(myarray, a)
end
end
However I get error:
BoundsError: attempt to access 500-element Array{Int64,1} at index [502]
How can I fix it (as efficiently as possible)?
Additional information. The above seems like a silly example, in my original problem I have a list of agents which interact. Therefore I am not sure if iterating over a copy would be the best solution. For example:
#creating my agent
mutable struct agent <: Any
id::Int
end
function delete_item!(myarray::Array{agent, 1}, item::agent)
deleteat!(myarray, findin(myarray, [item]))
end
#having my list of agents
n = 1000
myarray = agent[agent(i) for i = 1:n];
#trying to remove agents from list while having them interact
for a in myarray
#agent does stuff
if a.id%2 == 0 #if something happens remove
delete_item!(myarray, a)
end
end
Unfortunately there is no single answer to this question as most efficient approach depends on the logic of the whole model (in particular do other agents' actions depend on the fact that some entry is actually deleted from an array).
In most cases the following approach should be the simplest (I am leaving findin which is inefficient but I understand that you may have duplicates in myarray in general):
n = 1000
myarray = [i for i = 1:n];
keep = trues(n)
for (i, a) in enumerate(myarray)
keep[i] || continue # do not process an agent that is marked for deletion
if a%2 == 0 # here application logic might also need to check keep in some cases
keep[findin(myarray, [a])] = false
end
end
myarray = myarray[keep]
If for some reason you really need to delete elements of myarray in each iteration here is how you can do it:
n = 1000
myarray = [i for i = 1:n];
i = 1
while i <= length(myarray)
a = myarray[i]
if a%2 == 0
todelete = findin(myarray, [a])
i -= count(x -> x < i, todelete) # if myarray has duplicates of a you have to move the counter back
deleteat!(myarray, todelete)
else
i += 1
end
end
In general the code you give will not be very fast (e.g. if you know myarray does not contain duplicates it can be much simpler - and I guess you can).
EDIT: Here is how you can implement both versions if you know you do not have duplicates (you can simply use agent's index - observe that we can also avoid unnecessary checks):
n = 1000
myarray = [i for i = 1:n];
keep = trues(n)
for (i, a) in enumerate(myarray)
if a%2 == 0 # here application logic might also need to check keep in some cases
keep[i] = false
end
end
myarray = myarray[keep]
If for some reason you really need to delete elements of myarray in each iteration here is how you can do it:
n = 1000
myarray = [i for i = 1:n];
i = 1
while i <= length(myarray)
a = myarray[i]
if a%2 == 0
deleteat!(myarray, i)
else
i += 1
end
end
I'd like to write an iterator that behaves exactly like ipairs, except which takes a second argument. The second argument would be a table of the indices that ipairs should loop over.
I'm wondering if my current approach is inefficient, and how I could improve it with closures.
I'm also open to other methods of accomplishing the same thing. But I like iterators because they're easy to use and debug.
I'll be making references to and using some of the terminology from Programming in Lua (PiL), especially the chapter on closures (chapter 7 in the link).
So I'd like to have this,
ary = {10,20,30,40}
for i,v in selpairs(ary, {1,3}) do
ary[i] = v+5
print(string.format("ary[%d] is now = %g", i, ary[i]))
end
which would output this:
ary[1] is now = 15
ary[3] is now = 35
My current approach is this : (in order: iterator, factory, then generic for)
iter = function (t, s)
s = s + 1
local i = t.sel[s]
local v = t.ary[i]
if v then
return s, i, v
end
end
function selpairs (ary, sel)
local t = {}
t.ary = ary
t.sel = sel
return iter, t, 0
end
ary = {10,20,30,40}
for _,i,v in selpairs(ary, {1,3}) do
ary[i] = v+5
print(string.format("ary[%d] is now = %g", i, ary[i]))
end
-- same output as before
It works. sel is the array of 'selected' indices. ary is the array you want to perform the loop on. Inside iter, s indexes sel, and i indexes ary.
But there are a few glaring problems.
I must always discard the first returned argument s (_ in the for loop). I never need s, but it has to be returned as the first argument since it is the "control variable".
The "invariant state" is actually two invariant states (ary and sel) packed into a single table. Pil says that this is more expensive, and recommends using closures. (Hence my writing this question).
The rest can of this can be ignored. I'm just providing more context for what I'm wanting to use selpairs for.
I'm mostly concerned with the second problem. I'm writing this for a library I'm making for generating music. Doing simple stuff like ary[i] = v+5 won't really be a problem. But when I do stuff like accessing object properties and checking bounds, then I get concerned that the 'invariant state as a table' approach may be creating unnecessary overhead. Should I be concerned about this?
If anything, I'd like to know how to write this with closures just for the knowledge.
Of course, I've tried using closures, but I'm failing to understand the scope of "locals in enclosing functions" and how it relates to a for loop calling an iterator.
As for the first problem, I imagine I could make the control variable a table of s, i, and v. And at the return in iter, unpack the table in the desired order.
But I'm guessing that this is inefficient too.
Eventually, I'd like to write an iterator which does this, except nested into itself. My main data structure is arrays of arrays, so I'd hope to make something like this:
ary_of_arys = {
{10, 20, 30, 40},
{5, 6, 7, 8},
{0.9, 1, 1.1, 1.2},
}
for aoa,i,v in selpairs_inarrays(ary_of_arys, {1,3}, {2,3,4}) do
ary_of_arys[aoa][i] = v+5
end
And this too, could use the table approach, but it'd be nice to know how to take advantage of closures.
I've actually done something similar: A function that basically does the same thing by taking a function as it's fourth and final argument. It works just fine, but would this be less inefficient than an iterator?
You can hide "control variable" in an upvalue:
local function selpairs(ary, sel)
local s = 0
return
function()
s = s + 1
local i = sel[s]
local v = ary[i]
if v then
return i, v
end
end
end
Usage:
local ary = {10,20,30,40}
for i, v in selpairs(ary, {1,3}) do
ary[i] = v+5
print(string.format("ary[%d] is now = %g", i, ary[i]))
end
Nested usage:
local ary_of_arys = {
{10, 20, 30, 40},
{5, 6, 7, 8},
{0.9, 1, 1.1, 1.2},
}
local outer_indices = {1,3}
local inner_indices = {2,3,4}
for aoa, ary in selpairs(ary_of_arys, outer_indices) do
for i, v in selpairs(ary, inner_indices) do
ary[i] = v+5 -- This is the same as ary_of_arys[aoa][i] = v+5
end
end
Not sure if I understand what you want to achive but why not simply write
local values = {"a", "b", "c", "d"}
for i,key in ipairs {3,4,1} do
print(values[key])
end
and so forth, instead of implementing all that interator stuff? I mean your use case is rather simple. It can be easily extended to more dimensions.
And here's a co-routine based possibility:
function selpairs(t,selected)
return coroutine.wrap(function()
for _,k in ipairs(selected) do
coroutine.yield(k,t[k])
end
end)
end
I am having trouble figuring out how to get the length of a matrix within a matrix within a matrix (nested depth of 3). So what the code is doing in short is... looks to see if the publisher is already in the array, then it either adds a new column in the array with a new publisher and the corresponding system, or adds the new system to the existing array publisher
output[k][1] is the publisher array
output[k][2][l] is the system
where the first [] is the amount of different publishers
and the second [] is the amount of different systems within the same publisher
So how would I find out what the length of the third deep array is?
function reviewPubCount()
local output = {}
local k = 0
for i = 1, #keys do
if string.find(tostring(keys[i]), '_') then
key = Split(tostring(keys[i]), '_')
for j = 1, #reviewer_code do
if key[1] == reviewer_code[j] and key[1] ~= '' then
k = k + 1
output[k] = {}
-- output[k] = reviewer_code[j]
for l = 1, k do
if output[l][1] == reviewer_code[j] then
ltable = output[l][2]
temp = table.getn(ltable)
output[l][2][temp+1] = key[2]
else
output[k][1] = reviewer_code[j]
output[k][2][1] = key[2]
end
end
end
end
end
end
return output
end
The code has been fixed here for future reference: http://codepad.org/3di3BOD2#output
You should be able to replace table.getn(t) with #t (it's deprecated in Lua 5.1 and removed in Lua 5.2); instead of this:
ltable = output[l][2]
temp = table.getn(ltable)
output[l][2][temp+1] = key[2]
try this:
output[l][2][#output[l][2]+1] = key[2]
or this:
table.insert(output[l][2], key[2])
What I am trying to accomplish, is to be able to put some values inside an array, then based on a t (0-1), get a value out of the array based on its stored values.
To make this more clear, here's an example:
Array values = [0, 10]
Now this array would return value 0 for t=1 and value 10 for t=1. So t=.3 will give a value of 3.
Another example:
Array values = [10, 5, 5, 35]
t=.25 will give a value of 5
t=.125 will give a value of 7.5
Im looking for the most efficient formula to get the value at any given t using a given array.
Currently I'm using this (pseudo code)
var t:Number = .25;
var values:Array = [10, 5, 5, 35];
if(t == 1) value = [values.length-1];
else
var offset:Number = 1/values.length;
var startIndex:int = int(t/offset);
var fraction:Number = t % offset;
var roundPart:Number = (values[startIndex+1] - values[startIndex]) * fraction;
var value:Number = values[startIndex] + roundPart;
But i'm sure there's a far more better way of doing this. So i'm calling for the mathematicians on here!
Here is a One Liner in Mathematica. It's doing the same thing you are, only slightly more compact.
Arrays indexes start at 1.
values = {10, 5, 5, 35, 0}
f[a_, x_] := a[[k = IntegerPart[(k1 = (Dimensions[a][[1]] - 2) x)] + 1]] +
FractionalPart[k1] (a[[k + 1]] - a[[k]])
So your interpolation result on:
In[198]:= f[values,1]
Out[198]= 35
Etc.
If you plot changing the x scale: