Hi I have problem with matrix..
I have many .txt files with different number of rows but have the same number of column (1 column)
e.g. s1.txt = 1234 rows
s2.txt = 1200 rows
s2.txt = 1100 rows
I wanted to combine the three files. Since its have different rows .. when I write it to a new file I got this error = Index exceeds matrix dimensions.
How I can solved this problem? .
You can combine three matrices simply by stacking them: Assuming that s1, etc are the matrices you read in, you can make a new one like this:
snew = [s1; s2; s3];
You could also use the [] style stacking without creating the new matrix variable if you only need to do it once.
You have provided far too little information for an accurate diagnosis of your problem. Perhaps you have loaded the data from your files into variables in your workspace. Perhaps s1 has 1 column and 1234 rows, etc. Then you can concatenate the variables into one column vector like this:
totalVector = [s1; s2; s3];
and write it out to a file with a save() statement.
Does that help ?
Let me make an assumption that this question is connecting with your another question, and you want to combine those matrices by columns, leaving empty values in columns with fewer data.
In this case this code should work:
BaseFile ='s';
n=3;
A = cell(1,n);
for k=1:n
A{k} = dlmread([BaseFile num2str(k) '.txt']);
end
% create cell array with maximum number of rows and n number of columns
B = cell(max(cellfun(#numel,A)),n);
% convert each matrix in A to cell array and store in B
for k=1:n
B(1:numel(A{k}),k) = num2cell(A{k});
end
% save the data
xlswrite('output.txt',B)
The code assumes you have one column in each file, otherwise it will not work.
Related
I need to know if there is any efficient way of doing the following in MATLAB.
I have several big sparse matrices, the size of each one is roughly 9000000x9000000.
I need to access multiple element of such matrix and assign to each selected element a different value stored in another array. I'll give an example:
What I have:
SPARSE MATRIX of size 9000000x9000000
Matrix with the list of indexes and values I want to access, this is a matrix like this:
[row1, col1, value1;
row2, col2, value2;
...
rowN, colN, valueN]
Where N is the length of such matrix.
What I need:
Assign to the SPARSE MATRIX the corresponding value to the corresponding index, this is:
SPARSE_MATRIX(row1, col1) = value1
SPARSE_MATRIX(row2, col2) = value2
...
SPARSE_MATRIX(rowN, colN) = valueN
Thanks in advance!
EDIT:
Thank you to both for answering, I think I did not explain myself well, I'll try again.
I already have a large SPARSE MATRIX of about 9000000 rows x 9000000 columns, it is a SPARSE MATRIX filled with zeros.
Then I have another array or matrix, let's call it M with N number of rows, where N could take values from 0 to 9000000; and 3 columns. The first two columns are used to index an element of my SPARSE MATRIX, and the third column stores the value I want to transfer to the SPARSE MATRIX, this is, given a random row of M, i:
SPARSE_MATRIX(M(i, 1), M(i, 2)) = M(i, 3)
The idea is to do that for all the rows, I have tried it with common indexing:
SPARSE_MATRIX(M(:, 1), M(:, 2)) = M(:, 3)
Now I would like to do this assignation for all the rows in M as fast as possible, because if I use a loop or common indexing it takes ages (I am using a 7th Gen i7 processor with 16 GB of RAM). And I also need to keep the zeros in the SPARSE_MATRIX.
EDIT 2: SOLVED! Thank you Metahominid, I was not thinking through, but yes the sparse function does solve my problem, I just think my brain circuits were shortcircuited yesterday and was unable to see through it hahaha. Thank you to both anyway!
Regards!
You can construct a sparse matrix like this.
A = sparse(i,j,v)
S = sparse(i,j,v) generates a sparse matrix S from the triplets i, j,
and v such that S(i(k),j(k)) = v(k). The max(i)-by-max(j) output
matrix has space allotted for length(v) nonzero elements. sparse adds
together elements in v that have duplicate subscripts in i and j.
So you can simply construct the row vector, column vector and value vector.
I am answering in part because I cannot comment. You question seems a little confusing to me. The sparse() function in MATLAB does just this.
You can enter your arrays of indices and values directly into the interface, or declare a sparse matrix of zeros and set each individually.
Given your data format make three vectors, ROWS = [row1; ...; rown], COLS = [col1; ...; coln], and DATA = [val1; ... valn]. I am assuming that your size is the overall size of the full matrix and not the sparse portion.
Then
A = sparse(ROWS, COLS, DATA) will do just what you want. You can even specify the original matrix size.
A = sparse(ROWS, COLS, DATA, 90...., 90....).
I want to generate a 3D cell array called timeData so that timeData(:,:,a) for some integer a is an nx1 matrix of data, and the number of rows n varies with the value of a in a 1:1 correspondence. To do this, I am generating a 2D array of data called data that is nx1. This assignment statement takes place within a for loop as follows:
% Before iterating, I define an array of indices where I want to store the
% data sets in timeData. This choice of storage location is for
% organizational purposes.
A = [2, 5, 9, 21, 34, 100]; % Notice they are in ascending order, but have
% gaps that have no predictability.
sizeA = size(A);
numIter = A(1);
for m = 1:numIter % numIter is the number of data sets that I need to store
% in timeData
% At this point, some code that is entirely irrelevant to my question
% generates a nx1 array of data. One example of this data array is below.
data = [1.1;2.3;5.5;4.4]; % This is one example of what data could be. Its
% number of rows, n, changes each iteration, as
% do its contents.
B = size(data);
timeData(1:B(1),1,A(m)) = num2cell(data);
end
This code does put all contents of data in the appropriate locations within timeData as I want. However, it also adds {0x0 double} rows to all 2D arrays of timeData(:,:,a) for any a whose corresponding number of rows n was not the largest number of rows. Thus, there are many of these 2D arrays that have 10 to a couple hundred 0-valued rows that I don't want. For values of a that did not have a corresponding data set, the content of timeData(:,:,a) is an nx1 array of {0x0 double}.
I need to iterate over the contents of timeData in subsequent code, and I need to be able to find the size of the data set that is in timeData(:,:,a) without somehow discounting all the {0x0 double}.
How can I modify my assignment statement to fix this?
Edit: Desired output of the above example is the following with n = 5. Let this data set be represented by a = 9.
timeData(:,:,9) = {[1.1]}
{[2.3]}
{[5.5]}
{[8.6]}
{[4.4]}
Now, consider the possibility that a previous or subsequent value of the A matrix had a data set with n = 7, and n = 7 is the largest data set (largest n value). timeData(:,:,9) outputs like so in my code:
timeData(:,:,9) = {[1.1]}
{[2.3]}
{[5.5]}
{[8.6]}
{[4.4]}
{[0x0 double]}
{[0x0 double]}
#Dev-iL, as I understand it, your answer gives me the ability to delete the cells that have {[0x0 double]} in them (this is what I mean by "discounting"). This is a good plan B, but is there a way to prevent the {[0x0 double]} cells from showing up in the first place?
Edit 2: Update to the above statement "your answer gives me the ability to delete the cells that have {[0x0 double]} in them (this is what I mean by "discounting")". The cellfun(#isempty... ) function makes the {[0x0 double]}cells go to {[0x0 cell]}, it does not remove them. In other words, size(timeData(:,:,9)) is the same before and after the command is performed. This is not what I want. I want size(timeData(:,:,9)) to be 5x1 no matter what n is for any other value of a.
Edit 3: I just realized that the most desired output would be the following:
timeData(:,:,9) = {[1.1;2.3;5.5;8.6;4.4]} % An n x 1 column matrix within
% the cell.
but I can work with this outcome or the outcome as described above.
Unfortunately, I don't understand the structure of your dataset, which is why I can't suggest a better assignment method. However, I'd like to point out an operation that can you help deal with your data after it's been created:
cellfun(#isempty,timeData);
What the above does is return a logical array the size of timeData, indicating which cells contain something "empty". Typically, an array of arbitrary datatype is considered "empty" when it has at least one dimension that is equal to 0.
How can you use it to your advantage?
%% Example 1: counting non-empty cells:
nData = sum(~cellfun(#isempty,timeData(:)));
%% Example 2: assigning empty cells in place of empty double arrays:
timeData(cellfun(#isempty,timeData)) = {{}};
I have an Excel sheet containing 1838 records and I need to RANDOMLY split these records into 3 Excel Sheets. I am trying to use Matlab but I am quite new to it and I have just managed the following code:
[xlsn, xlst, raw] = xlsread('data.xls');
numrows = 1838;
randindex = ceil(3*rand(numrows, 1));
raw1 = raw(:,randindex==1);
raw2 = raw(:,randindex==2);
raw3 = raw(:,randindex==3);
Your general procedure will be to read the spreadsheet into some matlab variables, operate on those matrices such that you end up with three thirds and then write each third back out.
So you've got the read covered with xlsread, that results in the two matrices xlsnum and xlstxt. I would suggest using the syntax
[~, ~, raw] = xlsread('data.xls');
In the xlsread help file (you can access this by typing doc xlsread into the command window) it says that the three output arguments hold the numeric cells, the text cells and the whole lot. This is because a matlab matrix can only hold one type of value and a spreadsheet will usually be expected to have text or numbers. The raw value will hold all of the values but in a 'cell array' instead, a different kind of matlab data type.
So then you will have a cell array valled raw. From here you want to do three things:
work out how many rows you have (I assume each record is a row) by using the size function and specifying the appropriate dimension (again check the help file to see how to do this)
create an index of random numbers between 1 and 3 inclusive, which you can use as a mask
randindex = ceil(3*rand(numrows, 1));
apply the mask to your cell array to extract the records matching each index
raw1 = raw(:,randindex==1); % do the same for the other two index values
write each cell back to a file
xlswrite('output1.xls', raw1);
You will probably have to fettle the arguments to get it to work the way you want but be sure to check the doc functionname page to get the syntax just right. Your main concern will be to get the indexing correct - matlab indexes row-first whereas spreadsheets tend to be column-first (e.g. cell A2 is column A and row 2, but matlab matrix element M(1,2) is the first row and the second column of matrix M, i.e. cell B1).
UPDATE: to split the file evenly is surprisingly more trouble: because we're using random numbers for the index it's not guaranteed to split evenly. So instead we can generate a vector of random floats and then pick out the lowest 33% of them to make index 1, the highest 33 to make index 3 and let the rest be 2.
randvec = rand(numrows, 1); % float between 0 and 1
pct33 = prctile(randvec,100/3); % value of 33rd percentile
pct67 = prctile(randvec,200/3); % value of 67th percentile
randindex = ones(numrows,1);
randindex(randvec>pct33) = 2;
randindex(randvec>pct67) = 3;
It probably still won't be absolutely even - 1838 isn't a multiple of 3. You can see how many members each group has this way
numel(find(randindex==1))
I have observations txt file, number of files equals day in year.
Column 1 and 2 in txt files are time and obsearved results, some of them miss.
I want to combile 2nd column of each file within one big array.
I tried to create X Cell as big array. its size as (desired column, desired row)
and tried fill cell with a = X(:,1) but it's not solve.
How do I do this?
Presumably, the problem is that each file has a different number of elements.
Assuming the data from each file are in a cell array A, then you can form a new array as follows:
n = numel(A);
m = cellfun(#(x) size(x,1), A);
B = NaN(max(m), n);
for i = 1:n
B(1:m(i),i) = A{i}(:,2);
end
However, this doesn't align the times of the observations between the files. Comment if you need to do that too.
I'm just beginning to teach myself MATLAB, and I'm making a 501x6 array. The columns will contain probabilities for flipping 101 sided die, and as such, the columns contain 101,201,301 entries, not 501. Is there a way to 'stretch the column' so that I add 0s above and below the useful data? So far I've only thought of making a column like a=[zeros(200,1);die;zeros(200,1)] so that only the data shows up in rows 201-301, and similarly, b=[zeros(150,1);die2;zeros(150,1)], if I wanted 200 or 150 zeros to precede and follow the data, respectively in order for it to fit in the array.
Thanks for any suggestions.
You can do several thing:
Start with an all-zero matrix, and only modify the elements you need to be non-zero:
A = zeros(501,6);
A(someValue:someOtherValue, 5) = value;
% OR: assign the range to a vector:
A(someValue:someOtherValue, 5) = 1:20; % if someValue:someOtherValue is the same length as 1:20