I have big data files with currents and voltages. I measure several times my devices but the number of measurements varies. I first ask the user how many rounds of measurements there are, after which I make a loop to extract the currents from the data. My current variables are arrays of 200x3000 doubles. I call them for example Isd_round1, Isd_round2, etc...
for i=1:rounds_number
[filename,pathname]=uigetfile('*.mat', 'Select matlab data');
pathname = cd(pathname);
pathname = strcat(pathname, '\', filename);
Val=load(pathname);
assignin('base', ['Isd1_round' num2str(i)], Val.Isd1)
...etc...
end
After that, I want to plot and compare the currents, but I cannot seem to find a way to call the variables by changing the index. I would like to do something like this:
figure
hold on
for j=1:rounds_number
plot(V, Isd_roundj)
end
And I don't know how to call the variables by changing the index in the loop.
I could also do an array of all the currents but as each current is already an array of (n, m) doubles, how can I create a variable "current" where I would assign "Isd_round1" ?
I would recommend using a cell array to store the data, as was mentioned before. Here is some example code how, to do this:
dataCell = cell(rounds_number,1)
% read data in
for i=1:rounds_number
[filename,pathname]=uigetfile('*.mat', 'Select matlab data');
pathname = cd(pathname);
pathname = strcat(pathname, '\', filename);
Val=load(pathname);
dataCell{i} =Val
end
%plot
for i=1:rounds_number
plot(dataCell{i})
end
%quicker, warning this plots all rounds at once
cellfun(#(x) plot(x),dataCell)
Related
My code is posted below. It does exactly what I need it to do.
It reads in a file and plots the data that I need. If I want to read in another file and have it go through the same code, without having to write the whole thing a second time with different variables, is that possible? I would like to store the matrices from each loop.
As you can see the file I get is called: Oxygen_1keV_300K.xlsx
I have another file called: Oxygen_1keV_600K.xlsx
and so on.
How can I loop through these files without having to re-code the whole thing? I then want to plot them all on the same graph. It would be nice to store the final matrix Y and Ymean for each file so they are not overwritten.
clear
clc
files = ['Oxygen_1keV_300K','Oxygen_1keV_300K','Oxygen_1keV_600K','Oxygen_1keV_900K'];
celldata = cellstr(file)
k = cell(1,24);
for k=1:24
data{k} = xlsread('C:\Users\Ben\Desktop\Oxygen_1keV_300K.xlsx',['PKA', num2str(k)]);
end
for i=1:24
xfinal{i}=data{1,i}(end,1);
xi{i}=0:0.001:xfinal{i};
xi{i}=transpose(xi{i});
x{i}=data{1,i}(:,1);
y{i}=data{1,i}(:,4);
yi{i} = interp1(x{i},y{i},xi{i});
end
Y = zeros(10001, numel(data));
for ii = 1 : numel(data)
Y(:, ii) = yi{ii}(1 : 10001);
end
Ymean = mean(Y, 2);
figure (1)
x=0:0.001:10;
semilogy(x,Ymean)
Cell arrays make it very easy to store a list of strings that you can access as part of a for loop. In this case, I would suggest putting your file paths in a cell array as a substitute for the string used in your xlsread call
For example,
%The first file is the same as in your example.
%I just made up file names for the next two.
%Use the full file path if the file is not in your current directory
filepath_list = {'C:\Users\Ben\Desktop\Oxygen_1keV_300K.xlsx', 'file2.xlsx', 'file3.xlsx'};
%To store separate results for each file, make Ymean a cell array or matrix too
YMean = zeros(length(filepath_list), 1);
%Now use a for loop to loop over the files
for ii=1:length(filepath_list)
%Here's where your existing code would go
%I only include the sections which change due to the loop
for k=1:24
%The change is that on this line you use the cell array variable to load the next file path
data{k} = xlsread(filepath_list{ii},['PKA', num2str(k)]);
end
% ... do the rest of your processing
%You'll need to index into Ymean to store your result in the corresponding location
YMean(ii) = mean(Y, 2);
end
Cell arrays are a basic matlab variable type. For an introduction, I recommend the documentation for creating and accessing data in cell arrays.
If all your files are in the same directory, you can also use functions like dir or ls to populate the cell array programatically.
I am working in MATLAB for my image processing project.
I am using a for loop to generate some kind of image data (size of image varies) with each loop iteration. My problem is how do stop it from overwriting the image in next iteration.
Img(i,j)=data
Ideally I would like it to have
Img_1 = data (for 1st iteration)
Img_2 = data (for 2nd iteration)
Img_3 = data (for 3rd iteration)
and so on...
Is there any way, it can be acheived?
Yes, you can use dynamic field names with structures. I wouldn't recommend using separate variable names because your workspace will become unwieldy. Do something like this:
img_struct = struct(); %// Create empty structure
for ii = 1 : num_iterations
%// Do your processing on data
%...
%...
img_struct.(['Img_' num2str(ii)]) = data; %// After iteration
end
This will create a structure called img_struct where it will have fields that are named Img_1, Img_2, etc. To access a particular data from an iteration... say... iteration 1, do:
data = img_struct.Img_1;
Change the _1 to whatever iteration you choose.
Alternatively, you can use cell arrays... same line of thinking:
%// Create empty cell array
img_cell = cell(num_iterations, 1);
for ii = 1 : num_iterations
%// Do your processing on data
%...
%...
img_cell{ii} = data; %// After iteration
end
Cell arrays are arrays that take on any type per element - or they're non-homogeneous arrays. This means that each element can be whatever you want. As such, because your image data varies in size at each iteration, this will do very nicely. To access data at any iteration, simply do:
data = img_cell{ii};
ii is the index of the iteration you want to access.
If you want to literally obtain what you are asking for, you can use the eval() function, which takes a string as input that it will evaluate as if it were a line of code. Example:
for i=1:3
data=ones(i); % assign data, 'ones(i)' used as dummy for test
eval(['Img_' num2str(i) '=data;'])
end
However, I would recommend using cell arrays {}, or alternatively the struct function that rayryeng both suggested.
I'm new in matlab, I've searched a lot but I didn't find my answer. I want to get data from user in a for loop and put that data in matrix. I used this code:
npattern=inputdlg('Enter the number of Patterns');
a=npattern(1,1);
for i=1 : a(1,1);
r=inputdlg('Enter Data');
end
end
But it doesn't work for me. What should I do now?
Assuming your r can contain strings (not just numbers):
npattern=inputdlg('Enter the number of Patterns');
a=str2num(npattern{1});
for ii=1:a;
r{ii}=inputdlg('Enter Data');
end
Comments:
inputdlg returns a cell array of strings
it's bet not to use i as a variable (i is sqrt(-1) by default)
r in your code is overwritten at each iteration. Better use a cell array
there is one end too many
x=inputdlg('Enter the number of Patterns');
data = str2num(x{:});
r = zeros(data, 1);
for i=1:data
x = inputdlg('Enter Data');
r(i, 1) = str2num(x{:});
end
I need to calculate the mean, standard deviation, and other values for a number of variables and I was wondering how to use a loop to my advantage. I have 5 electrodes of data. So to calculate the mean of each I do this:
mean_ch1 = mean(ch1);
mean_ch2 = mean(ch2);
mean_ch3 = mean(ch3);
mean_ch4 = mean(ch4);
mean_ch5 = mean(ch5);
What I want is to be able to condense that code into a line or so. The code I tried does not work:
for i = 1:5
mean_ch(i) = mean(ch(i));
end
I know this code is wrong but it conveys the idea of what I'm trying to accomplish. I want to end up with 5 separate variables that are named by the loop or a cell array with all 5 variables within it allowing for easy recall. I know there must be a way to write this code I'm just not sure how to accomplish it.
You have a few options for how you can do this:
You can put all your channel data into one large matrix first, then compute the mean of the rows or columns using the function MEAN. For example, if each chX variable is an N-by-1 array, you can do the following:
chArray = [ch1 ch2 ch3 ch4 ch5]; %# Make an N-by-5 matrix
meanArray = mean(chArray); %# Take the mean of each column
You can put all your channel data into a cell array first, then compute the mean of each cell using the function CELLFUN:
meanArray = cellfun(#mean,{ch1,ch2,ch3,ch4,ch5});
This would work even if each chX array is a different length from one another.
You can use EVAL to generate the separate variables for each channel mean:
for iChannel = 1:5
varName = ['ch' int2str(iChannel)]; %# Create the name string
eval(['mean_' varName ' = mean(' varName ');']);
end
If it's always exactly 5 channels, you can do
ch = {ch1, ch2, ch3, ch4, ch5}
for j = 1:5
mean_ch(j) = mean(ch{j});
end
A more complicated way would be
for j = 1:nchannels
mean_ch(j) = eval(['mean(ch' num2str(j) ')']);
end
Apart from gnovice's answer. You could use structures and dynamic field names to accomplish your task. First I assume that your channel data variables are all in the format ch* and are the only variables in your MATLAB workspace. The you could do something like the following
%# Move the channel data into a structure with fields ch1, ch2, ....
%# This could be done by saving and reloading the workspace
save('channelData.mat','ch*');
chanData = load('channelData.mat');
%# Next you can then loop through the structure calculating the mean for each channel
flds = fieldnames(chanData); %# get the fieldnames stored in the structure
for i=1:length(flds)
mean_ch(i) = mean(chanData.(flds{i});
end
I am trying to deal with a very large dataset. I have k = ~4200 matrices (varying sizes) which must be compared combinatorially, skipping non-unique and self comparisons. Each of k(k-1)/2 comparisons produces a matrix, which must be indexed against its parents (i.e. can find out where it came from). The convenient way to do this is to (triangularly) fill a k-by-k cell array with the result of each comparison. These are ~100 X ~100 matrices, on average. Using single precision floats, it works out to 400 GB overall.
I need to 1) generate the cell array or pieces of it without trying to place the whole thing in memory and 2) access its elements (and their elements) in like fashion. My attempts have been inefficient due to reliance on MATLAB's eval() as well as save and clear occurring in loops.
for i=1:k
[~,m] = size(data{i});
cur_var = ['H' int2str(i)];
%# if i == 1; save('FileName'); end; %# If using a single MAT file and need to create it.
eval([cur_var ' = cell(1,k-i);']);
for j=i+1:k
[~,n] = size(data{j});
eval([cur_var '{i,j} = zeros(m,n,''single'');']);
eval([cur_var '{i,j} = compare(data{i},data{j});']);
end
save(cur_var,cur_var); %# Add '-append' when using a single MAT file.
clear(cur_var);
end
The other thing I have done is to perform the split when mod((i+j-1)/2,max(factor(k(k-1)/2))) == 0. This divides the result into the largest number of same-size pieces, which seems logical. The indexing is a little more complicated, but not too bad because a linear index could be used.
Does anyone know/see a better way?
Here's a version that combines going fast with using minimal memory.
I use fwrite/fread so that you still can use parfor (and this time, I made sure it works :) )
%# assume data is loaded an k is known
%# find the index pairs for comparisons. This could be done more elegantly, I guess.
%# I'm constructing a lower triangular array, i.e. an array that has ones wherever
%# we want to compare i (row) and j (col). Then I use find to get i and j
[iIdx,jIdx] = find(tril(ones(k,k),-1));
%# create a directory to store the comparisons
mkdir('H_matrix_elements')
savePath = fullfile(pwd,'H_matrix_elements');
%# loop through all comparisons in parallel. This way there may be a bit more overhead from
%# the individual function calls. However, parfor is most efficient if there are
%# a lot of relatively similarly fast iterations.
parfor ct = 1:length(iIdx)
%# make the comparison - do double b/c there shouldn't be a memory issue
currentComparison = compare(data{iIdx(ct)},data{jIdx{ct});
%# create save-name as H_i_j, e.g. H_104_23
saveName = fullfile(savePath,sprintf('H_%i_%i',iIdx(ct),jIdx(ct)));
%# save. Since 'save' is not allowed, use fwrite to write the data to disk
fid = fopen(saveName,'w');
%# for simplicity: save data as vector, add two elements to the beginning
%# to store the size of the array
fwrite(fid,[size(currentComparison)';currentComparison(:)]); % ' #SO formatting
%# close file
fclose(fid)
end
%# to read e.g. comparison H_104_23
fid = fopen(fullfile(savePath,'H_104_23'),'r');
tmp = fread(fid);
fclose(fid);
%# reshape into 2D array.
data = reshape(tmp(3:end),tmp(1),tmp(2));
You can get rid of the eval and clear calls by assigning the filename separately.
for i=1:k
[~,m] = size(data{i});
file_name = ['H' int2str(i)];
cur_var = cell(1, k-i);
for j=i+1:k
[~,n] = size(data{j});
cur_var{i,j} = zeros(m, n, 'single');
cur_var{i,j} = compare(data{i}, data{j});
end
save(file_name, cur_var);
end
If you need the saved variables to take different names, use the -struct option to save.
str.(file_name);
save(file_name, '-struct', str);