I have got a text file which contains 14000 rows and 7 columns. I have to take each of this columns. Then I have to find the sum of 1st 40 elements, then the next 40 elements(41-80) then the next 40 (81-120) and so on. I have written a MATLAB code for this. It is:
clc;clear all;close all;
fid = fopen('sks.txt');
datacell = textscan(fid,'%f%f%f%*[^\n]',...
'delimiter','\t');
fclose(fid);
A = datacell{1};
B=datacell{2};
l=size(A);
k=40;
sum=0;
for x=1:k
sum=sum+A(x);
end;
sum
for y=1:((l/k)-1)
sum1=0;
for i=((y*k)+1):((y+1)*k)
sum1=sum1+A(i);
end;
end;
I am getting all the sets of sums correcly with this code but I want all the answers as a single matrix. That is presently all the answers are obtained seperately. There are 350 seperate answers. I want all 350 in a single matrix. I want something like
Sum=23
34
87
.......
and so on.
Not
sum=23
sum=34
sum=87
I am not good at coding or MATLAB. So if there is a simpler way other than this you are more than welcome to give me that. Or please help me modify this code.:-)
You can assign those values in such a way (matrix will expand with every iteration):
sum = [] % init output matrix
for y=1:((l/k)-1)
sum1=0;
for i=((y*k)+1):((y+1)*k)
sum1=sum1+A(i);
end;
sum = [sum; sum1] % it will automatically expend matrix
end;
or as You know the final output of the Sum matrix (length(1:((l/k)-1)))
sum = zeros(1,length(1:((l/k)-1))) % init output matrix
ii = 1; % matrix index
for y=1:((l/k)-1)
sum1=0;
for i=((y*k)+1):((y+1)*k)
sum1=sum1+A(i);
end;
sum(ii) = sum1 % assign value to matrix
ii = ii + 1; % increment matrix index
end;
Not the whole answer - but will make the code much cleaner and faster:
You might run into some problems as sum is actually the name of a built-in function - which accidentally does exactly what you do in loops (just quicker).
Use stuff like:
mySum = sum(A)
and
mySum1 = mySum1 + sum( ((y*k)+1):((y+1)*k) )
Thanks for the answers guys. I got a simpler way. So I thought I will share it here. There is a command called reshape in matlab so I used it like this
A = datacell{1};
A1=squeeze( sum( reshape(A, 40, [], 1) ) );
A1 will give the sum of each set of 40 elements.
Related
I have the following data:
no_gridpoints = 640 % amount of columns in considered
surfaceelevation % a 1x640 array with surface elevation
Terskol1752, Terskol1753, ... Terskol2017 % 365x1 arrays with daily mean temperatures for 1 year of which the fifth colomn contains the temperature data
I want to create temp_glacier files with the corresponding year in the file name. This with a loop over all the years (1752-2017) by using the sprintf command in the loop:
for k = 1752:2017
for m = 1:no_gridpoints
sprintf('temp_glacier%d(m)',k) = sprintf('Terskol%d(:,5)',k) + surfaceelevation
end
end
However, I always get the error 'Subscripted assignment dimension mismatch.'. Can anyone tell me what I am doing wrong?
Thanks
As stated in my comment: it looks like you're mistaking sprintf for eval. The expression within sprintf is not evaluated, so your assignment is stating "make this string = this other string added to an array" - it makes no sense.
To correct your code as-is, you could do the following
for k = 1752:2017
for m = 1:no_gridpoints
eval(sprintf('temp_glacier%d(m) = Terskol%d(:,5) + surfaceelevation', k, k))
end
end
This is a bad idea
It would be far better practise for you to store your yearly data in a single cell array (or because it's numerical and the same size, just a standard matrix) rather than 266 individually named variables. I say better practise because if you to mean to use eval, you should know it should be avoided!
This method would look like the following:
Terskol = [ ... ] % your data here, in a 266*365 matrix where each row is a year
for k = (1752:2017) - 1751 % We actually want to loop through rows 1 to 266
for m = 1:no_gridpoints
% Your arrays were 1D, so you were originally getting a scalar temp val
% We can do that here like so...
temp_glacier(m) = Terskol(k, 5) + surfaceelevation;
% Now do something with temp_glacier, or there was no point in this loop!
% ...
end
end
Vectorising the inner loop:
for k = (1752:2017) - 1751 % We actually want to loop through rows 1 to 266
temp_glacier = repmat( Terskol(k, 5) + surfaceelevation, 1, no_gridpoints );
% Do something with temp_glacier...
end
I wrote this matlab code in order to concatenate the results of the integration of all the columns of a matrix extracted form a multi matrix array.
"datimf" is a matrix composed by 100 matrices, each of 224*640, vertically concatenated.
In the first loop i select every single matrix.
In the second loop i integrate every single column of the selected matrix
obtaining a row of 640 elements.
The third loop must concatenate vertically all the lines previously calculated.
Anyway i got always a problem with the third loop. Where is the error?
singleframe = zeros(224,640);
int_frame_all = zeros(1,640);
conc = zeros(100,640);
for i=0:224:(22400-224)
for j = 1:640
for k = 1:100
singleframe(:,:) = datimf([i+1:(i+223)+1],:);
int_frame_all(:,j) = trapz(singleframe(:,j));
conc(:,k) = vertcat(int_frame_all);
end
end
end
An alternate way to do this without using any explicit loops (edited in response to rayryeng's comment below. It's also worth noting that using cellfun may not be more efficient than explicitly looping.):
nmats = 100;
nrows = 224;
ncols = 640;
datimf = rand(nmats*nrows, ncols);
% convert to an nmats x 1 cell array containing each matrix
cellOfMats = mat2cell(datimf, ones(1, nmats)*nrows, ncols);
% Apply trapz to the contents of each cell
cellOfIntegrals = cellfun(#trapz, cellOfMats, 'UniformOutput', false);
% concatenate the results
conc = cat(1, cellOfIntegrals{:});
Taking inspiration from user2305193's answer, here's an even better "loop-free" solution, based on reshaping the matrix and applying trapz along the appropriate dimension:
datReshaped = reshape(datimf, nrows, nmats, ncols);
solution = squeeze(trapz(datReshaped, 1));
% verify solutions are equivalent:
all(solution(:) == conc(:)) % ans = true
I think I understand what you want. The third loop is unnecessary as both the inner and outer loops are 100 elements long. Also the way you have it you are assigning singleframe lots more times than necessary since it does not depend on the inner loops j or k. You were also trying to add int_frame_all to conc before int_frame_all was finished being populated.
On top of that the j loop isn't required either since trapz can operate on the entire matrix at once anyway.
I think this is closer to what you intended:
datimf = rand(224*100,640);
singleframe = zeros(224,640);
int_frame_all = zeros(1,640);
conc = zeros(100,640);
for i=1:100
idx = (i-1)*224+1;
singleframe(:,:) = datimf(idx:idx+223,:);
% for j = 1:640
% int_frame_all(:,j) = trapz(singleframe(:,j));
% end
% The loop is uncessary as trapz can operate on the entire matrix at once.
int_frame_all = trapz(singleframe,1);
%I think this is what you really want...
conc(i,:) = int_frame_all;
end
It looks like you're processing frames in a video.
The most efficent approach in my experience would be to reshape datimf to be 3-dimensional. This can easily be achieved with the reshape command.
something along the line of vid=reshape(datimf,224,640,[]); should get you far in this regard, where the 3rd dimension is time. vid(:,:,1) then would display the first frame of the video.
Hi for my code I would like to know how to best save my variable column. column is 733x1. Ideally I would like to have
column1(y)=column, but I obtain the error:
Conversion to cell from logical is not possible.
in the inner loop. I find it difficult to access these stored values in overlap.
for i = 1:7
for y = 1:ydim % ydim = 436
%execute code %code produces different 'column' on each iteration
column1{y} = column; %'column' size 733x1 %altogether 436 sets of 'column'
end
overlap{i} = column1; %iterates 7 times.
end
Ideally I want overlap to store 7 variables saved that are (733x436).
Thanks.
I'm assuming column is calculated using a procedure where each column is dependent on the latter. If not, then there are very likely improvements that can be made to this:
column = zeros(733, 1); % Might not need this. Depends on you code.
all_columns = zeros(xdim, ydim); % Pre-allocate memory (always do this)
% Note that the first dimension is usually called x,
% and the second called y in MATLAB
overlap = cell(7, 1);
overlap(:) = {zeros(xdim, ydim)}; % Pre-allocate memory
for ii = 1:numel(overlap) % numel is better than length
for jj = 1:ydim % ii and jj are better than i and j
% several_lines_of_code_to_calculate_column
column = something;
all_columns(:, jj) = column;
end
overlap{ii} = all_columns;
end
You can access the variables in overlap like this: overlap{1}(1,1);. This will get the first element in the first cell. overlap{2} will get the entire matrix in the second cell.
You specified that you wanted 7 variables. Your code implies that you know that cells are better than assigning it to different variables (var1, var2 ...). Good! The solution with different variables is bad bad bad.
Instead of using a cell array, you could instead use a 3D-array. This might make processing later on faster, if you can vectorize stuff for instance.
This will be:
column = zeros(733, 1); % Might not need this. Depends on you code.
overlap = zeros(xdim, ydim, 7) % Pre-allocate memory for 3D-matrix
for ii = 1:7
for jj = 1:ydim
% several_lines_of_code_to_calculate_column
column = something;
all_column(:, jj, ii) = column;
end
end
I would like to divide a vector in many vectors and put all of them in a matrix. I got this error "Subscripted assignment dimension mismatch."
STEP = zeros(50,1);
STEPS = zeros(50,length(locate));
for i = 1:(length(locate)-1)
STEP = filtered(locate(i):locate(i+1));
STEPS(:,i) = STEP;
end
I take the value of "filtered" from (1:50) at the first time for example and I would like to stock it in the first row of a matrix, then for iterations 2, I take value of "filtered from(50:70) for example and I stock it in row 2 in the matrix, and this until the end of the loop..
If someone has an idea, I don't get it! Thank you!
As mentioned in the comments, to make it work you can edit the loopy code at the end with -
STEPS(1:numel(STEP),i) = STEP;
Also, output array STEPS doesn't seem to use the last column. So, the initialization could use one less column, like so -
STEPS = zeros(50,length(locate)-1);
All is good with the loopy code, but in the long run with a high level language like MATLAB, you might want to look for faster codes and one way to achieve that would be vectorized codes. So, let me suggest a vectorized solution using bsxfun's masking capability to process such ragged-arrays. The implementation to cover generic elements in locate would look something like this -
% Get differentiation, which represent the interval lengths for each col
diffs = diff(locate)+1;
% Initialize output array
out = zeros(max(diffs),length(locate)-1);
% Get elements from filtered array for setting into o/p array
vals = filtered(sort([locate(1):locate(end) locate(2:end-1)]));
% Use bsxfun to create a mask that are to be set in o/p array and set thereafter
out(bsxfun(#ge,diffs,(1:max(diffs)).')) = vals;
Sample run for verification -
>> % Inputs
locate = [6,50,70,82];
filtered = randi(9,1,120);
% Get extent of output array for number of rows
N = max(diff(locate))+1;
>> % Original code with corrections
STEP = zeros(N,1);
STEPS = zeros(N,length(locate)-1);
for i = 1:(length(locate)-1)
STEP = filtered(locate(i):locate(i+1));
STEPS(1:numel(STEP),i) = STEP;
end
>> % Proposed code
diffs = diff(locate)+1;
out = zeros(max(diffs),length(locate)-1);
vals = filtered(sort([locate(1):locate(end) locate(2:end-1)]));
out(bsxfun(#ge,diffs,(1:max(diffs)).')) = vals;
>> max_error = max(abs(out(:)-STEPS(:)))
max_error =
0
I am trying to concatenate several structs. What I take from each struct depends on a function that requires a for loop. Here is my simplified array:
t = 1;
for t = 1:5 %this isn't the for loop I am asking about
a(t).data = t^2; %it just creates a simple struct with 5 data entries
end
Here I am doing concatenation manually:
A = [a(1:2).data a(1:3).data a(1:4).data a(1:5).data] %concatenation function
As you can see, the range (1:2), (1:3), (1:4), and (1:5) can be looped, which I attempt to do like this:
t = 2;
A = [for t = 2:5
a(1:t).data
end]
This results in an error "Illegal use of reserved keyword "for"."
How can I do a for loop within the concatenate function? Can I do loops within other functions in Matlab? Is there another way to do it, other than copy/pasting the line and changing 1 number manually?
You were close to getting it right! This will do what you want.
A = []; %% note: no need to initialize t, the for-loop takes care of that
for t = 2:5
A = [A a(1:t).data]
end
This seems strange though...you are concatenating the same elements over and over...in this example, you get the result:
A =
1 4 1 4 9 1 4 9 16 1 4 9 16 25
If what you really need is just the .data elements concatenated into a single array, then that is very simple:
A = [a.data]
A couple of notes about this: why are the brackets necessary? Because the expressions
a.data, a(1:t).data
don't return all the numbers in a single array, like many functions do. They return a separate answer for each element of the structure array. You can test this like so:
>> [b,c,d,e,f] = a.data
b =
1
c =
4
d =
9
e =
16
f =
25
Five different answers there. But MATLAB gives you a cheat -- the square brackets! Put an expression like a.data inside square brackets, and all of a sudden those separate answers are compressed into a single array. It's magic!
Another note: for very large arrays, the for-loop version here will be very slow. It would be better to allocate the memory for A ahead of time. In the for-loop here, MATLAB is dynamically resizing the array each time through, and that can be very slow if your for-loop has 1 million iterations. If it's less than 1000 or so, you won't notice it at all.
Finally, the reason that HBHB could not run your struct creating code at the top is that it doesn't work unless a is already defined in your workspace. If you initialize a like this:
%% t = 1; %% by the way, you don't need this, the t value is overwritten by the loop below
a = []; %% always initialize!
for t = 1:5 %this isn't the for loop I am asking about
a(t).data = t^2; %it just creates a simple struct with 5 data entries
end
then it runs for anyone the first time.
As an appendix to gariepy's answer:
The matrix concatenation
A = [A k];
as a way of appending to it is actually pretty slow. You end up reassigning N elements every time you concatenate to an N size vector. If all you're doing is adding elements to the end of it, it is better to use the following syntax
A(end+1) = k;
In MATLAB this is optimized such that on average you only need to reassign about 80% of the elements in a matrix. This might not seam much, but for 10k elements this adds up to ~ an order of magnitude of difference in time (at least for me).
Bare in mind that this works only in MATLAB 2012b and higher as described in this thead: Octave/Matlab: Adding new elements to a vector
This is the code I used. tic/toc syntax is not the most accurate method for profiling in MATLAB, but it illustrates the point.
close all; clear all; clc;
t_cnc = []; t_app = [];
N = 1000;
for n = 1:N;
% Concatenate
tic;
A = [];
for k = 1:n;
A = [A k];
end
t_cnc(end+1) = toc;
% Append
tic;
A = [];
for k = 1:n;
A(end+1) = k;
end
t_app(end+1) = toc;
end
t_cnc = t_cnc*1000; t_app = t_app*1000; % Convert to ms
% Fit a straight line on a log scale
P1 = polyfit(log(1:N),log(t_cnc),1); P_cnc = #(x) exp(P1(2)).*x.^P1(1);
P2 = polyfit(log(1:N),log(t_app),1); P_app = #(x) exp(P2(2)).*x.^P2(1);
% Plot and save
loglog(1:N,t_cnc,'.',1:N,P_cnc(1:N),'k--',...
1:N,t_app,'.',1:N,P_app(1:N),'k--');
grid on;
xlabel('log(N)');
ylabel('log(Elapsed time / ms)');
title('Concatenate vs. Append in MATLAB 2014b');
legend('A = [A k]',['O(N^{',num2str(P1(1)),'})'],...
'A(end+1) = k',['O(N^{',num2str(P2(1)),'})'],...
'Location','northwest');
saveas(gcf,'Cnc_vs_App_test.png');