I am still a newbe and I have probabily a very easy question concerning arrays of matrices. I have a matrix of nrows like the following one:
>> matrix
1 678 543
2 676 541
3 543 987
4 543 98
1 433 54
2 908 32
3 457 54
4 235 21
How to create arrays of equal size matrices?
i.e array{i,1}
This is replication of question:
Array of Matrices in MATLAB
and probably of many others.
What is not clear to me, is how to populate my array of fixed dimension matrices. So that
>>array{1,1}
1 678 543
2 676 541
3 543 987
4 543 98
Here is my attempt:
Find all the ones in column 1 of matrix and the size of matrix.
Create cell arrays, look in each line, if it is equal to 1 create an array{i,1} of zeros equal to the size of the matrices I want to create (in my case 4x3).
If not equal to 1 insert into the array the first four values of matrix.
Is there any faster way to do it without a loop?
You can also use mat2cell:
mat2cell(matrix, [4 4])
Related
Consider that I have a code that returns a double array. When run, the result returned at the command window a result looks like this:
mpc.gen=
1 100 344 34 5
2 433 223 45 2
3 333 432 12 3
4 213 233 12 3
What I want to do is create a MATLAB script which would contain this array. In other words in this new MATLAB script I would have the following array, constructed like this:
mpc.gen= [ 1 100 344 34 5 ;
2 433 223 45 2 ;
3 333 432 12 3 ;
4 213 233 12 3 ;
] ;
Just calling the function would save the variable in the new script, however that is not what I need since I need to use this script for a simulation at a special power tool called MATPOWER. The array needs to be in the form shown at the new script.
The actual array is much bigger in size however I use this here for simplicity. Is there any way I can do this automatically, and not just pass the data from the command window to the new script one by one manually? Any help would be greatly appreciated. Thank you in advance for your time!
What you want to use is mat2str. It converts a matrix to a string representation that, when evaluated, results in the identical matrix.
For example:
>> result = [1 100 344 34 5;
2 433 223 45 2;
3 333 432 12 3;
4 213 233 12 3];
>> mat2str(result)
ans =
[1 100 344 34 5;2 433 223 45 2;3 333 432 12 3;4 213 233 12 3]
You could write this to a file like so:
f = fopen('test_script.m', 'w');
fprintf(f,'mpc.gen = %s\n', mat2str(result));
fclose(f);
The formatting is not identical to your example, but if the tool does proper MATLAB parsing, it shouldn't be a problem.
Is it intentional that mpc is a struct? (you are using dot in the name.) In the following, I use underscore instead, but it can certainly be adopted, if it is intentional.
This is what functions are for. So instead of making a script, you should create a new function. If I were to do what you want to do, I would have 2 functions and 1 script. Whereas the script looks like this
mpc_bus = function1;
function2(mpc_bus);
where function1 is the code that returns mpc.bus and function2 is the one where you want to work with mpc.gen, and the top would be something like this
function [] = function2(mpc_gen)
Alternatively: If you of some reason does not like functions, you can make the first code save the variable using save(*filename*.mat) and then you can load the file again in the script using dat=load(*filename*.mat); and mpc_gen = dat.mpc_bus;
I am new to using Julia and have little experience with the language. I am trying to understand how multi-dimensional arrays work in it and how to access the array at the different dimensions. The documentation confuses me, so maybe someone here can explain it better.
I created an array (m = Array{Int64}(6,3)) and am trying to access the different parts of that array. Clearly I am understanding it wrong so any help in general about Arrays/Multi-Dimensional Arrays would help.
Thanks
Edit I am trying to read a file in that has the contents
58 129 10
58 129 7
25 56 10
24 125 25
24 125 15
13 41 10
0
The purpose of the project is to take these fractions (58/129) and round the fractions using farey sequence. The last number in the row is what both numbers need to be below. Currently, I am not looking for help on how to do the problem, just how to create a multidimensional array with all the numbers except the last row (0). My trouble is how to put the numbers into the array after I have created it.
So I want m[0][0] = 58, so on. I'm not sure how syntax works for this and the manual is confusing. Hopefully this is enough information.
Julia's arrays are not lists-of-lists or arrays of pointers. They are a single container, with elements arranged in a rectangular shape. As such, you do not access successive dimensions with repeated indexing calls like m[j][i] — instead you use one indexing call with multiple indices: m[i, j].
If you trim off that last 0 in your file, you can just use the built-in readdlm to load that file into a matrix. I've copied those first six rows into my clipboard to make it a bit easier to follow here:
julia> str = clipboard()
"58 129 10\n58 129 7\n25 56 10\n24 125 25\n24 125 15\n13 41 10"
julia> readdlm(IOBuffer(str), Int) # or readdlm("path/to/trimmed/file", Int)
6×3 Array{Int64,2}:
58 129 10
58 129 7
25 56 10
24 125 25
24 125 15
13 41 10
That's not very helpful in teaching you how Julia's arrays work, though. Constructing an array like m = Array{Int64}(6,3) creates an uninitialized matrix with 18 elements arranged in 6 rows and 3 columns. It's a bit easier to see how things work if we fill it with a sensible pattern:
julia> m .= [10,20,30,40,50,60] .+ [1 2 3]
6×3 Array{Int64,2}:
11 12 13
21 22 23
31 32 33
41 42 43
51 52 53
61 62 63
This has set up the values of the array to have the row number in their tens place and the column number in the ones place. Accessing m[r,c] returns the value in m at row r and column c.
julia> m[2,3] # second row, third column
23
Now, r and c don't have to be integers — they can also be vectors of integers to select multiple rows or columns:
julia> m[[2,3,4],[1,2]] # Selects rows 2, 3, and 4 across columns 1 and 2
3×2 Array{Int64,2}:
21 22
31 32
41 42
Of course ranges like 2:4 are just vectors themselves, so you can more easily and efficiently write that example as m[2:4, 1:2]. A : by itself is a shorthand for a vector of all the indices within the dimension it indexes into:
julia> m[1, :] # the first row of all columns
3-element Array{Int64,1}:
11
12
13
julia> m[:, 1] # all rows of the first column
6-element Array{Int64,1}:
11
21
31
41
51
61
Finally, note that Julia's Array is column-major and arranged contiguously in memory. This means that if you just use one index, like m[2], you're just going to walk down that first column. As a special extension, we support what's commonly referred to as "linear indexing", where we allow that single index to span into the higher dimensions. So m[7] accesses the 7th contiguous element, wrapping around into the first row of the second column:
julia> m[5],m[6],m[7],m[8]
(51, 61, 12, 22)
I have some sample code where the array is sliced as follows:
A = X(:,2:300)
What does this mean about the slice of the array?
: stands for 'all' if used by itself and 2:300 gives an array of integers from 2 to 300 with a spacing of 1 (1 is implicit) in MATLAB. 2:300 is the same as 2:1:300 and you can even use any spacing you wish, for example 2:37:300 (result: [2 39 76 113 150 187 224 261 298]) to generate equally spaced numbers.
Your statement says - select every row of the matrix A and columns 2 to 300. Suggested reading
I have two double arrays like the ones below:
K>> var_conx
var_conx =
1
3
127
129
216
217
252
253
302
303
342
343
and
K>> var_cony
var_cony =
2
126
128
216
217
252
253
302
303
342
343
My task is pretty simple, I only need to store in an another double array all the common values of the two arrays, let's call the other array "common_convar".
To be specific, for the two arrays above, i only want to store the values 216,217,252,253,302,303,342,343. For the other values, i do not care and i do not want them stored or whatever.
I have written the following code:
for i=1:length(var_conx)
for j=1:length(var_cony)
if var_conx(i)==var_cony(j)
common_convar(i,:)=[var_conx(i)];
end
end
end
The problem i encountered here is that the array common_convar also stores some zeros in the beginning:
K>> common_convar
common_convar =
0
0
0
0
216
217
252
253
302
303
342
343
How is it possible to get rid of zeros and only store the desired common values of the two arrays var_conx and var_cony?
Thanks in advance for your time.
Firstly you could find the elements common to both arrays, without having to do nested loops, using the Matlab set intersect function:
common_values= intersect(var_conx,var_cony);
Then you could find the nonzero elements of the common array via logical indexing:
common_values = common_values(common_values > 0);
I have an array that has some calcultations done on the second column. I would like the values from the third column to follow/be linked to the second column.
Test Code:
a1= [1,10,-11;
2,70,232;
3,33.2,-33;
4,40,44;]
a2calc=abs(a1(:,2)-max(a1(:,2))) %calculation
a2=[a1(:,1),a2calc,a1(:,3)] %new array
Example:
original a1 Array
1 10 -11
2 70 232
3 33.2 -33
4 40 44
a2 Array after column 2 calculations looks like this
1 60 -11
2 0 232
3 36.8 -33
4 30 44
I'm trying to get the final array to look like this (column 3 values follow / are linked to the second column)
1 60 232
2 0 -11
3 36.8 44
4 30 -33
What I'm having problems with is I'm not sure if I should use the index values of column 2 and if so how I can get it to look like the final output array I included in the question.
I might be wrong here, but it looks to me like the logic is:
After calculating the second column, change the order of the third column so that the third column is sorted the same way as the second. To see what I mean:
This represents the two columns, numbered from highest to lowest:
A = 1 1
4 3
2 2
3 4
If I understand it right, you want the resulting matrix to be
A = 1 1
4 4
2 2
3 3
If this is the right logic then you should check out sort with two outputs. You can use the second output to index the third column.
[~, idx] = sort(A(:, 2));
sorted_3 = sort(A(:, 3));
A(idx, 3) = sorted_3;
The output from this is:
A =
1.00000 60.00000 232.00000
2.00000 0.00000 -33.00000
3.00000 36.80000 44.00000
4.00000 30.00000 -11.00000
Good luck!