I have a struct array named Lst. Every struct has the following form:
Point (x,y)
Type (1-6)
I want get the separate array of points for each type. How can I get it?
Lst(Lst.Type==1);
won't work since Type is not a field of Lst but of Lst(i).
In addition, is there a way to save the indexes of each item or an alternative way to then combine them again to the original order?
L1 = Lst([Lst.Type]==1); will give you the subset L1 of Lst where Type == 1.
Likewise, you can use idx1 = find([Lst.Type]==1) to memorize your indexes.
EDIT: the above uses the [] operator to aggregate the field elements Type of Lst into an array. To your comment/question, you could use the exact same operator also to obtain an array of specific field elements X of a subset of the structured array, as in
X1 = [Lst([Lst.Type]==1).X];
Related
If I define my array like this:
array[_, 1..2] of J: A;
where J is a enum, what function can I use to get the length of the first dimension of A? The length function returns 14 (and states that it doesn't work for multiple dimensions). I had it hard-coded like so in my testing, but it won't always be 13:
constraint forall(row in 1..13)(S[A[row, 2]] >= C[A[row, 1]]);
The length function is really only meant for getting the number of elements. When you want the retrieve indexes of an array, you should instead use the index_set function. This returns the actual index set, which you can iterate over: i in index_set(A)
For multidimensional arrays there are specific functions for each index set of the array. For example, to get the first index set from a two-dimensional array (as in your code fragment) you can use the function index_set_1of2
I have a structure in Matlab, each field contains elements with varying numbers of variables. I would like to remove duplicates of numbers that appear within the same field: I know the unique() function and know how to use it to scan through fields one at a time but not an entire field.
I think I want something like:
structure(1:length(structure)).field=unique(structure(1:length(structure)).field
and get
original
field=[1,2,3] [1,4,5] [2,5,8]
to turn into
field=[1,2,3] [4,5] [8]
Maybe a complicated for loop similar to below (isn't working) which would grab the values from the first element in the field, search through each additional element, and if that value is present set it equal to =[];, and iterate through that way?
for n=1:length(RESULTS)
for m=1:length(RESULTS(n).Volumes)
for l=1:length(RESULTS)
for o=1:length(RESULTS(l).Volumes)
if RESULTS(n).Volumes(m)==RESULTS(l).Volumes(o)
RESULTS(l).Volumes(o)=[];
end
end
end
end
end
Thanks!
This is a quick-and-dirty attempt, but you might be able to improve on it. Assume your struct array and field are sa(:).v. I'm also assuming that the field contains a 1xn array of numbers, as in your example. First, make a "joint" array with the concatenation of all field values and filter the non-unique values:
joint = cell2mat({sa.v});
[uniqJoint,~,backIdx] = unique(joint);
The "uniqJoint" array has also been sorted, but the "backIdx" array contains the indices that, if applied to uniqJoint, will rebuild the original "joint" array. We need to somehow connect those to the original indices (i,j) into the struct array and within the field value sa(i).v(j). To do that, I tried creating an array of the same size as "joint" that contains the indices of the struct that originally had the corresponding element in the "joint" array:
saIdx = cell2mat(arrayfun(#(i) i * ones(1,length(sa(i).v)), ...
1:length(sa), 'UniformOutput', false));
Then you can edit (or, in my case, copy and modify the copy of) the struct array to set the field to the values that have not appeared before. To do that, I keep a logical array to mark the indices of "backIdx" as "already used", in which case I skip those values when rebuilding the fields of each struct:
sb = sa;
used = false(length(backIdx));
for i = 1:length(sa)
origInd = find(saIdx == i); % Which indices into backIdx correspond to this struct?
newInd = []; % Which indices will be used?
for curI = backIdx(origInd)
if ~used(curI)
% Mark as used and add to the "to copy" list
used(curI) = true;
newInd(end+1) = curI;
end
end
% Rewrite the field with only the indices that were not used before
sb(i).v = uniqJoint(newInd);
end
In the end, the data in sb(i).v contains the same numbers as sa(i).v without repeats, and removing those that appeared in any previous elements of the struct.
I am trying to create an array where each element is an empty array.
I have tried this:
var result = Array.fill[Array[Int]](Array.empty[Int])
After looking here How to create and use a multi-dimensional array in Scala?, I also tried this:
var result = Array.ofDim[Array[Int]](Array.empty[Int])
However, none of these work.
How can I create an array of empty arrays?
You are misunderstanding Array.ofDim here. It creates a multidimensional array given the dimensions and the type of value to hold.
To create an array of 100 arrays, each of which is empty (0 elements) and would hold Ints, you need only to specify those dimensions as parameters to the ofDim function.
val result = Array.ofDim[Int](100, 0)
Array.fill takes two params: The first is the length, the second the value to fill the array with, more precisely the second parameter is an element computation that will be invoked multiple times to obtain the array elements (Thanks to #alexey-romanov for pointing this out). However, in your case it results always in the same value, the empty array.
Array.fill[Array[Int]](length)(Array.empty)
Consider also Array.tabulate as follows,
val result = Array.tabulate(100)(_ => Array[Int]())
where the lambda function is applied 100 times and for each it delivers an empty array.
I have a Matlab structure like this:
Columns.T21=6;
Columns.ws21=9;
Columns.wd21=10;
Columns.u21=11;
Is there some elegant way I can give the value and return the field name? For instance, if I give 6 and it would return 'T21.' I know that fieldnames() will return all the field names, but I want the fieldname for a specific value. Many thanks!
Assuming that the structure contains fields with scalar numeric values, you can use this struct2array based approach -
search_num = 6; %// Edit this for a different search number
fns=fieldnames(Columns) %// Get field names
out = fns(struct2array(Columns)==search_num) %// Logically index into names to find
%// the one that matches our search
Goal:
Construct two vectors from your struct, one for the names of fields and the other for their respective values. This has analogy to the dict in Python or map in C++, where you have unique keys being mapped to possibly non-unique values.
Simple Solution:
You can do this very simply using the various functions defined for struct in Matlab, namely: struc2cell() and cell2mat()
For the particular element of interest, say 1 of your struct Columns, get the names of all fields in the form of a cell array, using fieldnames() function:
fields = fieldnames( Columns(1) )
Similarly, get the values of all the fields of that element of Columns, in the form of a matrix
vals = cell2mat( struct2cell( Columns(1) ) )
Next, find the field with the corresponding value, say 6 here, using the find function and convert the resulting 1x1 cell into a char using cell2mat() function :
cell2mat( fields( find( vals == 6 ) ) )
which will yield:
T21
Now, you can define a function that does this for you, e.g.:
function fieldname = getFieldForValue( myStruct, value)
Advanced Solution using Map Container Data Abstraction:
You can also choose to define an object of the containers.map class using the field-names of your struct as the keySet and values as valueSet.
myMap = containers.Map( fieldnames( Columns(1) ), struct2cell( Columns(1) ) );
This allows you to get keys and values using corresponding built-in functions:
myMapKeys = keys(myMap);
myMapValues = values(myMap);
Now, you can find all the keys corresponding to a particular value, say 6 in this case:
cell2mat( myMapKeys( find( myMapValues == 6) )' )
which again yields:
T21
Caution: This method, or for that matter all methods for doing so, will only work if all the fields have the values of the same type, because the matrix to which we are converting vals to, need to have a uniform type for all its elements. But I assume from your example that this would always be the case.
Customized function/ logic:
struct consists of elements that contain fields which have values, all in that order. An element is thus a key for which field is a value. The essence of "lookup" is to find values (which are non-unique) for specific keys (which are unique). Thus, Matlab has a built-in way of doing so. But what you want is the other way around, i.e. to find keys for specific values. Since its not a typical use case, you need to write up your own logic or function for it.
Suppose your structure is called S. First extract all the field names into an array:
fNames=fieldnames(S);
Now define a following anonymous function in your code:
myfun=#(yourArray,desiredValue) yourArray==desiredValue;
Then you can get the desired field name as:
desiredFieldIndex=myfun(structfun(#(x) x,S),3) %desired value is 3 (say)
desiredFieldName=fNames(desiredFieldIndex)
Alternative using containers.Map
Assuming each field in the structure contains one scalar value as in the question (not an array).
Aim is to create a Map object with the field values as keys and the field names as values
myMap = containers.Map(struct2cell(Columns),fieldnames(Columns))
Now to get the fieldname for a value index into myMap with the value
myMap(6)
ans =
T21
This has the advantage that if the structure doesn't change you can repeatedly use myMap to find other value-field name pairs
As input to a function, I am getting an array of target elements, T, and an array of structs S where each one has a .elems field, which is a list of integers (elements).
I'm sure there's a simple way to do this in Matlab. How do I get the indices i of all structs where a specific element t of T is in S(i).elems contains t?
So I think you'll need to do this with an arrayfun. I did:
S = ... (1-by-N array of structs);
T = ... (1-by-K array of numbers);
indices = find(arrayfun(#(i)any(ismember(T, S(i).elems)), 1:numel(S)));
any(ismember(T, S(i)elems)) tests is any of the things in T are in S(i).elems. The arrayfun repeats this for each struct in S. find extracts indices from the logical array that is returned by the arrayfun.