I have following cell array:
res{1}.nft.x=1;
res{2}.nft.x=2;
res{3}.nft.x=3;
How can I easily get an array of nft.x values, i.e., [1 2 3] in this case?
Thanks!
use cellfun
>> cellfun( #(x) x.nft.x, res )
Use comma-separated lists (a very powerful feature in MATLAB):
v = [res{:}];
v = [v.nft];
v = [v.x];
Of course, this only works if all structures have the identical fields. If not, you'll have to resort to a loop or something similar, for instance:
cellfun(#(x)x.nft.x, res)
the latter may seem a bit more elegant, but it's definitely much slower for a larger data set.
Clarification
res{:} creates a comma separated list of structs, and [res{:}] concatenates them into an array. Accessing a field of an array of structs again results in a comma separated list, hence the additional concatenation, field access and yet another concatenation.
Related
Basically, I’m given a list of strings such as:
["structA.structB.myArr[6].myVar",
"structB.myArr1[4].myArr2[2].myVar",
"structC.myArr1[3][4].myVar",
"structA.myArr1[4]",
"structA.myVar"]
These strings are describing variables/arrays from multiple structs. The integers in the arrays describe the size each array. Given a string has a/multiple arrays (1d or 2d), I want to generate a list of strings which go through each index combination in the array for that string. I thought of using for loops but issue is I don’t know how many arrays are in a given string before running the script. So I couldn’t do something like
for i in range (0, idx1):
for j in range (0, idx2):
for k in range (0, idx3):
arr.append(“structA.myArr1[%i][%i].myArr[%i]” %(idx1,idx2,idx3))
but the issue is that I don’t know how I can create multiple/dynamic for loops based on how many indexes and how I could create a dynamic append statement that changes per each string from the original list since each string will have a different number of indexes and the arrays will be in different locations of the string.
I was able to write a regex to find all the index for each string in my list of strings:
indexArr = re.findall('\[(.*?)\]', myString)
//after looping, indexArr = [['6'],['4','2'],['3','4'],['4']]
however I'm really stuck on how to achieve the "dynamic for loops" or use recursion for this. I want to get my ending list of strings to look like:
[
["structA.structB.myArr[0].myVar",
"structA.structB.myArr[1].myVar",
...
"structA.structB.myArr[5].myVar”],
[“structB.myArr1[0].myArr2[0].myVar",
"structB.myArr1[0].myArr2[1].myVar",
"structB.myArr1[1].myArr2[0].myVar",
…
"structB.myArr1[3].myArr2[1].myVar”],
[“structC.myArr1[0][0].myVar",
"structC.myArr1[0][1].myVar",
…
"structC.myArr1[2][3].myVar”],
[“structA.myArr1[0]”,
…
"structA.myArr1[3]”],
[“structA.myVar”] //this will only contain 1 string since there were no arrays
]
I am really stuck on this, any help is appreciated. Thank you so much.
The key is to use itertools.product to generate all possible combinations of a set of ranges and substitute them as array indices of an appropriately constructed string template.
import itertools
import re
def expand(code):
p = re.compile('\[(.*?)\]')
ranges = [range(int(s)) for s in p.findall(code)]
template = p.sub("[{}]", code)
result = [template.format(*s) for s in itertools.product(*ranges)]
return result
The result of expand("structA.structB.myArr[6].myVar") is
['structA.structB.myArr[0].myVar',
'structA.structB.myArr[1].myVar',
'structA.structB.myArr[2].myVar',
'structA.structB.myArr[3].myVar',
'structA.structB.myArr[4].myVar',
'structA.structB.myArr[5].myVar']
and expand("structB.myArr1[4].myArr2[2].myVar") is
['structB.myArr1[0].myArr2[0].myVar',
'structB.myArr1[0].myArr2[1].myVar',
'structB.myArr1[1].myArr2[0].myVar',
'structB.myArr1[1].myArr2[1].myVar',
'structB.myArr1[2].myArr2[0].myVar',
'structB.myArr1[2].myArr2[1].myVar',
'structB.myArr1[3].myArr2[0].myVar',
'structB.myArr1[3].myArr2[1].myVar']
and the corner case expand("structA.myVar") naturally works to produce
['structA.myVar']
I need to create an array filled within a range in Matlab
e.g.
from=2
to=6
increment=1
result
[2,3,4,5,6]
e.g.
from=15
to=25
increment=2
result
[15,17,19,21,23,25]
Obviously I can create a loop to perform this action from scratch but I wondering if there is a coincise and efficent way to do this with built-in matlab commands since seems a very common operation
EDIT
If I use linspace the operation is weird since the spacing between the points is (x2-x1)/(n-1).
This can be handled simply by the : operator in the following notation
array = from:increment:to
Note that the increment defaults to 1 if written with only one colon seperator
array = from:to
Example
array1 = 2:6 %Produces [2,3,4,5,6]
array2 = 15:2:25 %Produces [15,17,19,21,23,25]
I have an n-dimensional array A and want to slice it dynamically, i.e., given a list of array dimensions, like [2 4], and a list of values, like [6 8], I want
B = A(:,6,:,8,:,:,:,:,...)
List lengths are unknown. Using eval would work but is not an option. This question is a generalization of a previous post to multiple indices and dimensions without a for-loop.
You can still use the previous post I linked to (which I originally flagged as a duplicate) to answer your question. This original post only slices in one dimension. I originally flagged it as a duplicate and closed it because all you need to do is replace one line of code in the original post's accepted answer to achieve what you want. However, because it isn't that obvious, I have decided to reopen the question and answer the question for you.
Referring to the previous post, this is what Andrew Janke (the person with the accepted answer on the linked post) did (very clever I might add):
function out = slice(A, ix, dim)
subses = repmat({':'}, [1 ndims(A)]);
subses{dim} = ix;
out = A(subses{:});
Given a matrix A, an index number ix and the dimension you want to access dim, the above function would equivalently perform:
out = A(:, :, ..., ix, :, :,...:);
^ ^ ^ ^
dimensions --> 1 2 dim dim+1
You would access your desired dimension in dim, and place what value you want to use to slice into that dimension. As such, you'd call it like this:
out = slice(A, ix, dim);
How the function works is that subses would generate a cell array of ':' strings (that will eventually be converted into ':' operators) that is as long as the total number of dimensions of A. Next, you would access the element at dim, which corresponds to the dimension you want and you would replace this with ix. You would then unroll this cell array so that we would access A in the manner that you see in the above equivalent statement.
Who would have thought that you can use strings to index into an array!?
Now, to generalize this, all you have to do is make one small but very crucial change. ix would now be a vector of indices, and dim would be a vector of dimensions you want to access. As such, it would look something like this:
function out = slice(A, ix, dim)
subses = repmat({':'}, [1 ndims(A)]);
subses(dim) = num2cell(ix);
out = A(subses{:});
The only difference we see here is the second line of the code. We have to use num2cell so that you can convert each element into a cell array, and we slice into this cell array to replace the : operators with your desired dimensions. Note that we are using () braces and not {} braces. () braces are used to slice through cell arrays while {} are used to access cell array contents. Because we are going to assign multiple cells to subses, () is needed. We then perform our slicing in A accordingly.
As such, given your problem and with the above modifications, you would do:
out = slice(A, [6 8], [2 4]);
Be advised that ix and dim must contain the same number of elements and they must be 1D. Also, ix and dim should be sensible inputs (i.e. not floating point and negative). I don't do this error checking because I'm assuming you know what you're doing and you're smart enough to know how to use this properly.
Good luck!
What is the most elegant way to reduce elementwise-conditions in multidimensional-arrays to one logical variable in Matlab? I need this for a big project with a lot of if conditions and assertions. In the Matlab documentation about logical arrays and find array elements there is no satifying solution for this problem.
For example, a logical variable myBool is true iff there are two ones at the same position in the matrices A and B:
A = [0,1;0,0]
B = [0,1;1,0]
My preferred solution so far is:
myBool = any(A(:)==1 & B(:)==1)
But it doesn't look like the shortest solution and it doesn't work with array indexing.
A shorter but not very readable solution:
myBool = any(A(B==1))
The biggest problem is that for higher dimensional arrays the functions like nnz() only reduce the order by one dimension without the colon (:), but with the colon it is not possible to index a part of the array...
Firstly, if you use matrices of class logical, then you don't need to test for equality to 1.
Indexing aside, the best approach would be:
bFlag = any(A(:) & B(:));
If you need indexing, you have two options. You can use a small vectorising anonymous function:
fhVec = #(T)(T(:));
bFlag = any(fhVec(A(rowIndices, colIndices) & B(rowIndices, colIndices)));
alternatively, you can use linear indexing:
vnLinearIndices = sub2ind(size(A), rowIndices, colIndices);
bFlag = any(A(vnLinearIndices) & B(vnLinearIndices));
Going nuts with cell array, because I just can't get rid of it... However, it will be an easy one for you guys out here.
So here is why:
I have a dataset (data) which contains two variables: A (Numbers) and B (cell array).
Unfortunately I can't even reconstruct the problem nevertheless my imported table looks like this:
data=dataset;
data.A = [1;1;3;3;3];
data.B = ['A';'A';'BUU';'BUU';'A'];
where data.B is of the type 5x1 cell which I can't reconstruct
all I want now is the unique rows like
ans= [1 A;3 BUU;3 A]
the result should be in a dataset or just two vectors where the rows are equivalent.
but unique([dataA dataB],'rows') can't handle cell arrays and I can't find anywhere in the www how I simple convert the cell array B to a vector of strings (does it exist?).
cell2mat() didn't work for me, because of the different word length ('A' vs 'BUU').
Though, two things I would love to learn: Making an 5x1 cell to an string vector
and find unique rows out of numbers and strings (or cells).
Thank you very much!
Cheers Dominik
The problem is that the A and B fields are of a different type. Although they could be concatenated into a cell array, unique can't handle that. A general trick for cases like this is to "translate" elements of each field (column) to unique identifiers, i.e. numbers. This translation can be done applying unique to each field separately and getting its third output. The obtained identifiers can now be concatenated into a matrix, so that each row of this matrix is a "composite identifier". Finally, unique with 'rows' option can be applied to this matrix.
So, in your case:
[~, ~, kA] = unique(data.A);
[~, ~, kB] = unique(data.B);
[~, jR] = unique([kA kB], 'rows');
Now build the result as (same format as data)
result.A = data.A(jR);
result.B = data.B(jR);
or as (2D cell array)
result = cat(2, mat2cell(data.A(jR), ones(1,numel(jR))), data.B(jR));
Here is my clumpsy solution
tt.A = [1;1;3;3;3];
tt.B = {'A';'A';'BUU';'BUU';'A'};
Convert integers to characters, then merge and find unique strings
tt.C = cellstr(num2str(tt.A));
tt.D = cellfun(#(x,y) [x y],tt.C,tt.B,'UniformOutput',0);
[tt.F,tt.E] = unique(tt.D);
Display results
tt.F