I have the following example which expresses the type of problem that I'm trying to solve:
clear all
textdata = {'DateTime','St','uSt','Ln','W'};
data = rand(365,4);
Final = struct('data',data,'textdata',{textdata})
clear textdata data
From this, Final.data contains values which correspond to the headings in Final.textdata excluding the first ('DateTime') thus Final.data(:,1) corresponds to the heading 'St'... and so on. What I'm trying to do is to create a variable in the workspace for each of these vectors. So, I would have a variable for St, uSt, Ln, and W in the workspace with the corresponding values given in Final.data.
How could this be done?
Will this solve your problem:
for ii=2:length( textdata )
assignin('base',Final.textdata{ii},Final.data(:,ii-1));
end
Let me know if I misunderstood.
The direct answer to your question is to use the assignin function, like so (edit: just like macduff suggested 10 minutes ago):
%Starting with a Final structure containing the data, like this
Final.textdata = {'DateTime','St','uSt','Ln','W'};
Final.data = rand(365,4);
for ix = 1:4
assignin('base',Final.textdata{ix+1}, Final.data(:,ix));
end
However, I strongly discourage using dynamic variable names to encode data like this. Code that starts this way usually ends up as spaghetti code full of long string concatenations and eval statements. Better is to use a structure, like this
for ix = 1:4
dataValues(Final.textdata{ix+1}) = Final.data(:,ix);
end
Or, to get the same result in a single line:
dataValues = cell2struct(num2cell(Final.data,1), Final.textdata(2:end),2)
Related
I am beginner in MATLAB. I would like to load 200 image files (size 192x192) in a specific folder by using a for loop.
The image names are '1.png', '2.png', '3.png' and so on.
My code is as below.
list = dir('C:/preds/*.png');
N = size(list,1);
sum_image = zeros(192,192,200);
for i = 1:N
sum_image(:,:,i) = imread('C:/preds/i.png');
end
Which part should I change ?
I would probably do it like the code below:
You are currently getting the list of filenames then not really doing much with it. Iterating over the list is safer otherwise if there is a missing number you could have issues. Also, the sort maybe unnecessary depending if you image numbering is zero-padded so they come out in the correct order ... but better safe than sorry. One other small change initializing the array to size N instead of hard-coding 200. This will make it more flexible.
searchDir = 'C:\preds\';
list = dir([searchDir '*.png']);
nameList = {list.name}; %Get array of names
imNum = str2double(strrep(nameList,'.png','')); %Get image number
[~,idx] = sort(imNum); %sort it
nameList = nameList(idx);
N = numel(nameList);
sum_image = zeros(192,192,N);
for i=1:N
sum_image(:,:,i) = imread(fullfile(searchDir,nameList{i}));
end
I would suggest changing the line within the loop to the following:
sum_image(:,:,i) = imread(['C:/preds/', num2str(i), '.png']);
MATLAB treats the i in your string as a character and not the variable i. The above line of code builds your string piece by piece.
If this isn't a homework problem, the right answer to this question is don't write this as a for loop. Use an imageDatastore:
https://www.mathworks.com/help/matlab/ref/imagedatastore.html
ds = imageDatastore('C:/preds/');
sumImageCellArray = readall(ds);
sumImage = cat(3,sumImageCellArray{:});
I have an excel file and I need to read it based on string values in the 4th column. I have written the following but it does not work properly:
[num,txt,raw] = xlsread('Coordinates','Centerville');
zn={};
ctr=0;
for i = 3:size(raw,1)
tf = strcmp(char(raw{i,4}),char(raw{i-1,4}));
if tf == 0
ctr = ctr+1;
end
zn{ctr}=raw{i,4};
end
data=zeros(1,10); % 10 corresponds to the number of columns I want to read (herein, columns 'J' to 'S')
ctr=0;
for j = 1:length(zn)
for i=3:size(raw,1)
tf=strcmp(char(raw{i,4}),char(zn{j}));
if tf==1
ctr=ctr+1;
data(ctr,:,j)=num(i-2,10:19);
end
end
end
It gives me a "15129x10x22 double" thing and when I try to open it I get the message "Cannot display summaries of variables with more than 524288 elements". It might be obvious but what I am trying to get as the output is 'N = length(zn)' number of matrices which represent the data for different strings in the 4th column (so I probably need a struct; I just don't know how to make it work). Any ideas on how I could fix this? Thanks!
Did not test it, but this should help you get going:
EDIT: corrected wrong indexing into raw vector. Also, depending on the format you might want to restrict also the rows of the raw matrix. From your question, I assume something like selector = raw(3:end,4); and data = raw(3:end,10:19); should be correct.
[~,~,raw] = xlsread('Coordinates','Centerville');
selector = raw(:,4);
data = raw(:,10:19);
[selector,~,grpidx] = unique(selector);
nGrp = numel(selector);
out = cell(nGrp,1);
for i=1:nGrp
idx = grpidx==i;
out{i} = cell2mat(data(idx,:));
end
out is the output variable. The key here is the variable grpidx that is an output of the unique function and allows you to trace back the unique values to their position in the original vector. Note that unique as I used it may change the order of the string values. If that is an issue for you, use the setOrderparameter of the unique function and set it to 'stable'
I have a loop which runs 100 times. In each iteration there is a string, double and a table assigned, and in the next iteration new values are assigned for them. What I want to do is to accumulate these values and after the loop finishes save the total result as result.mat using the matlab save function. I've tried putting them in cell-array but its not working so far, so if anyone could please advise how this can be done.
This is what I did:
results_cell=(100,3);
.
.
.
results_cell(i,1)=stringA;
results_cell(i,2)=TableA;
results_cell(i,3)=DoubleA;
But it gives this error Coversion to Cell from Table is not possible. So I've tried converting TableA to array of Doubles using table2array but I still get this Coversion to Cell from Double is not possible
I think using a structure would be a good way to store your data, since they are of different types and you can assign it meaningful field names for easy reference.
For example, let's call the structure Results. You can initialize it like so.
Results = struct('StringData',[],'TableData',[],'DoubleData',[])
Since you know its dimensions, you can even do this:
N = 100;
Results(N).StringData = [];
Results(N).TableData = [];
Results(N).DoubleData = [];
This automatically create a 1xN structure with 3 fields.
Then in your loop you can assign each field with its associated data like so:
for k = 1:N
Results(k).StringData = String(k);
Results(k).TableData = Table(k);
Results(k).DoubleData = Double(k);
end
where String(k), Table(k) and Double(k) are just generic names for your actual data.
When you're done with the loop you can access any type of data using a single index and the right field name.
In order to save a .mat file, use something like this:
save SomeFileName.mat Results
Which you can load into the workspace as you would with any .mat file:
Eg:
S = load('SomeFileName.mat')
R = S.Results
Hope that helps!
I need to output .mat files for the below data. I need one file to have cell (1,1) to be Mean_RPM_list1, cell (2,1) to be Mean_RPM_list2 etc. And then I need another file to have cell(1,1) to be Mean_Torque_list1 to have cell(1,1).....and so on.
Can anybody shed any light on this for me?
Also if someone knows how to automate me calling the matrices A and B so I could have A = [Mean_rpm1:Mean_rpmMAX], that would also be very helpful.
TIA for any help.
A = [Mean_rpm1 Mean_rpm2 Mean_rpm3 Mean_rpm4 Mean_rpm5 Mean_rpm6 Mean_rpm7 Mean_rpm8 Mean_rpm9 Mean_rpm10 Mean_rpm11 Mean_rpm12];
B = [Mean_torque1 Mean_torque2 Mean_torque3 Mean_torque4 Mean_torque5 Mean_torque6 Mean_torque7 Mean_torque8 Mean_torque9 Mean_torque10 Mean_torque11 Mean_torque12];
plot(A,B,'*')
for i = 1:num_bins;
bin = first + ((i-1)/10);
eval(sprintf('Mean_RPM_list%0.f = A;',bin*10));
eval(sprintf('Mean_Torque_list%0.f = B;',bin*10));
end
First of all this is really bad idea to create a set of variables with names different by numbers. As you can see it's very difficult to deal with such variables, you always have to use eval (or other related) statements.
It's much easier to create a cell array Mean_rpm and access its elements as Mean_rpm{1}, etc.
If the vectors are numeric and have the same size you can also make a 2D/3D array. Then access as Mean_rpm(:,:,1) etc.
Next, to store a cell array to a mat-file you have to create this array in MATLAB. No options (at least for now) to do it by parts in a loop. (But you can do it for numeric vectors and matrices using matfile object.) So why do you need this intermediate Mean_RPM_list variable? Just do Mean_RPM_list{bin*10} = A in your loop.
For your first question, if you already have those variables you have to use eval in a loop. Something like
A = [];
for k=1:K
eval(sprintf('A{k} = [A, Mean_rpm%d];',k));
end
You can also get names for all similar variables and combine them.
varlist = who('Mean_rpm*');
A = cell(1,numel(varlist);
for k = 1:numel(varlist)
eval('A{k} = varlist{k};');
end
Here is one without loop using CELL2FUN:
A=cellfun(#(x)evalin('base',x),varlist,'UniformOutput',0);
You should avoid having all these individual variables around in the first place. Data types like arrays, cell arrays and structure arrays exist to help you with this. If you want each variable to be associated with a name, you can use a structure array. I've made an example below. Instead of assigning a value to Mean_rpm1 like you are doing now, assign it to meanStruct.Mean_rpm1 then save the entire structure.
% as you generate values for each variable, assign them to the
% appropriate field.
meanStruct.Mean_rpm1 = [10:10];
meanStruct.Mean_rpm2 = [12:15];
meanStruct.Mean_rpm3 = [13:20];
meanStruct.Mean_rpm4 = [14];
meanStruct.Mean_rpm5 = [15:18];
meanStruct.Mean_rpm6 = [16:20];
meanStruct.Mean_rpm7 = [17:22];
meanStruct.Mean_rpm8 = [18:22];
meanStruct.Mean_rpm9 = [19:22];
meanStruct.Mean_rpm10 = [20:22];
meanStruct.Mean_rpm11 = [21:22];
meanStruct.Mean_rpm12 = [22:23];
% save the structure array
save('meanValues.mat','meanStruct')
% load and access the structure array
clear all
load('meanValues.mat')
temp = meanStruct.Mean_rpm3
I was just wondering if there is a clean way to store a matrix after each iteration with a different name? I would like to be able to store each matrix (uMatrix) under a different name depending on which simulation I am on eg Sim1, Sim2, .... etc. SO that Sim1 = uMatrix after first run through, then Sim2 = uMatrix after 2nd run through. SO that each time I can store a different uMatrix for each different Simulation.
Any help would be much appreciated, and sorry if this turns out to be a silly question. Also any pointers on whether this code can be cleaned up would be great too
Code I am using below
d = 2;
kij = [1,1];
uMatrix = [];
RLABEL=[];
SimNum = 2;
for i =1:SimNum
Sim = ['Sim',num2str(i)] %Simulation number
for j=1:d
RLABEL = [RLABEL 'Row','',num2str(j) ' '];
Px = rand;
var = (5/12)*d*sum(kij);
invLam = sqrt(var);
u(j) = ((log(1-Px))*-invLam)+kij(1,j);
uMatrix(j,1) = j;
uMatrix(j,2) = u(j);
uMatrix(j,3) = kij(1,j);
uMatrix(j,4) = Px;
uMatrix(j,5) = invLam;
uMatrix(j,6) = var;
end
printmat(uMatrix,'Results',RLABEL,'SECTION u kij P(Tij<u) 1/Lambda Var')
end
There are really too many options. To go describe both putting data into, and getting data our of a few of these methods:
Encode in variable names
I really, really dislike this approach, but it seems to be what you are specifically asking for. To save uMatrix as a variable Sim5 (after the 5th run), add the following to your code at the end of the loop:
eval([Sim ' = uMatrix;']); %Where the variable "Sim" contains a string like 'Sim5'
To access the data
listOfStoredDataNames = who('Sim*')
someStoredDataItem = eval(listOfStoredDataNames {1}) %Ugghh
%or of you know the name already
someStoredDataItem = Sim1;
Now, please don't do this. Let me try and convince you that there are better ways.
Use a structure
To do the same thing, using a structure called (for example) simResults
simResults.(Sim) = uMatrix;
or even better
simResults.(genvarname(Sim)) = uMatrix;
To access the data
listOfStoredDataNames = fieldnames(simResults)
someStoredDataItem = simResults.(listOfStoredDataNames{1})
%or of you know the name already
someStoredDataItem = simResults.Sim1
This avoids the always problematic eval statement, and more importantly makes additional code much easier to write. For example you can easily pass all simResults into a function for further processing.
Use a Map
To use a map to do the same storage, first initialize the map
simResults = containers.Map('keyType','char','valueType','any');
Then at each iteration add the values to the map
simResults(Sim) = uMatrix;
To access the data
listOfStoredDataNames = simResults.keys
someStoredDataItem = simResults(listOfStoredDataNames{1})
%or of you know the name already
someStoredDataItem = simResults('Sim1')
Maps are a little more flexible in the strings which can be used for names, and are probably a better solution if you are comfortable.
Use a cell array
For simple, no nonsense storage of the results
simResults{i} = uMatrix;
To access the data
listOfStoredDataNames = {}; %Names are Not available using this method
someStoredDataItem = simResults{1}
Or, using a slight level of nonesense
simResults{i,1} = Sim; %Store the name in column 1
simResults{i,2} = uMatrix; %Store the result in column 2
To access the data
listOfStoredDataNames = simResults(:,1)
someStoredDataItem = simResults{1,2}
Just to add to the detailed answer given by #Pursuit, there is one further method I am fond of:
Use an array of structures
Each item in the array is a structure which stores the results and any additional information:
simResults(i).name = Sim; % store the name of the run
simResults(i).uMatrix = uMatrix; % store the results
simResults(i).time = toc; % store the time taken to do this run
etc. Each element in the array will need to have the same fields. You can use quick operations to extract all the elements from the array, for example to see the timings of each run at a glance you can do:
[simResults.time]
You can also use arrayfun to to a process on each element in the array:
anon_evaluation_func = #(x)( evaluate_uMatrix( x.uMatrix ) );
results = arrayfun( anon_evaluation_func, simResults );
or in a more simple syntax,
for i = 1:length(simResults)
simResults(i).result = evaluate_uMatrix( simResults(i).uMatrix );
end
I would try to use a map which stores a <name, matrix>.
the possible way to do it would be to use http://www.mathworks.com/help/matlab/map-containers.html