Suppose I have different rows loaded from a .mat file (using load filename.mat) containing float numbers following the same naming convention, e.g:
file_3try = [ 2.4, 5.2, 7.8 ]
file_4try = [ 8.7, 2.5, 4,2 ]
file_5try = [ 11.2, 9.11 ]
to plot all of these in one plot using automation (I have many more rows than in the example above) I created a cell containing the names of the arrays by using:
name{l} = sprintf('%s%02i%s','file_',num,'try');
inside a for loop with num the numbers in the names and l a counter starting from 1.
But when I try to plot the arrays using for example:
plot(name{1})
I get the error:
Error using plot
Invalid first data argument
Is there a way to solve this, or am I going about this wrong?
There is something built in to solve this
data = load ( 'filename' ); % load data and store in struct
fnames = fieldnames ( data );
for ii=1:length(fnames)
plot ( axHandle, data.(fnames{ii}) );
end
axHandle is a handle to the axes you want to plot on. Its not required but it is good practice to use it. If its not provided then the plot command will plot on the current axes, e.g. gca.
So as mentioned already you need to use eval.
Assuming the file_**X**try rows are different lengths then you could just place all of them in a cell rather than creating a cell of the variable names. So instead of assigning to separate variables the way you are doing you could assign to a cell, so:
file_try{i} = [.....];
You can then cycle through file_try and plot each entry:
for i = 1:length(file_try)
plot(file_try{i});
end
If the rows are not different lengths then stick them in a matrix and plot it.
Related
I wrote a main function in Matlab that calls other functions, each of which produces plots in a new figure. Though each function produces different plots (different colors, number of subplots, and so on) they all share some features (font, fontsize, Linewidth etc.).
In order to make it easier to modify the aforementioned shared parameter for all the MATLAB figures, I have defined in the preamble of the main function a structure variable as follows:
var.font = 'Arial Unicode MS';
var.fontsize = 13;
var.interpreter = 'none' ;
and so on for the other fields. When I call the function in this way (providing the structure as input):
function plot1( var , ... )
fig = gcf
fig.Position(3) = var.Position3
fig.Position(4) = var.Position4
end
everything works fine and the functions apply the feature to each figure. But if I try to provide a variable number of input to the functions using varargin, in this way
function plot1( varargin )
fig = gcf;
temp = varargin(1);
fig.Position(3) = temp.Position3;
fig.Position(4) = temp.Position4;
end
The following error message is prompted "Struct contents reference from a non-struct array object."
You're indexing the cell array incorrectly (this is easily done).
Round parentheses ( ) give you a cell output when indexing a cell array - i.e. your temp is a 1x1 cell with the struct inside it.
You need curly braces { } to extract the contents of a cell array.
Fix: use curly braces:
temp = varargin{1};
I sometimes think of cell arrays as a group of boxes, since each element (or "box" in this analogy) can basically contain anything. To extract a subset of boxes, use round parentheses. To extract the contents of the boxes, use braces. This analogy extends also to tables, where the notation is consistent.
Here's some docs on indexing cell arrays, where the difference is described in more detail:
https://uk.mathworks.com/help/matlab/matlab_prog/access-data-in-a-cell-array.html
I am working with a 400x1200 imported table (readtable generated from an .xls) which contains strings, doubles, dates, and NaNs. Each column is typed consistently. I am looking for a way to locate all instances in the table of any given string ('Help me please') and replace them all with a double (1). Doing this in Matlab will save me loads of work making changes to the approach used on the rest of this project.
Unfortunately, all of the options I've looked at (regexp, strrep, etc) can only take a string as a replacement. Strfind was similarly unhelpful, because of the typing across the table. The lack of cellfun has also made this harder than it should be. I know the solution should have something to do with finding the indices of the strings I want and then just looping DataFile{subscript} = [1], but I can't find a way to do it.
First you should transform your table at a cell array.
Then, you can use the strrep along with str2num, e.g.
% For a given cell index
strrep(yourCellIndexVariable, "Help me please", "1");
str2num(yourCellIndexVariable);
This will replace the string "Help me please" with the string "1" (the strrep function) and the str2num will change the cell index to the double value according to the string.
By yourCellIndexVariable I mean an element from the cell array. There are several ways to get all cells from a cell array, but I think that you have solved that part already.
What you can do is as follows:
[rows, cols] = size(table); % Get the size of your table
YourString = 'Help me please'; % Create your string
Strmat = repmat(YourString,rows,cols); % Stretch to fill a matrix of table size
TrueString = double(strcmp(table,Strmat)); % Compares all entries with one another
TrueString now contains logicals, 1 where the string 'Help me please' is located, and 0 where it is not.
If you have a table containing multiple classes it might be handy to switch to cells though.
Thank you very much everyone for helping think through to a solution. Here's what I ended up with:
% Reads data
[~, ~, raw] = xlsread ( 'MyTable.xlsx');
MyTable = raw;
% Makes a backup of the data in table form
MyTableBackup = readtable( 'MyTable.xlsx' );
% Begin by ditching 1st row with variable names
MyTable(1,:) = [];
% wizard magic - find all cells with strings
StringIndex = cellfun('isclass', MyTable, 'char');
% strrep goes here to recode bad strings. For example:
MyTable(StringIndex) = strrep(MyTable(StringIndex), 'PlzHelpMe', '1');
% Eventually, we are done, so convert back to table
MyTable = cell2table(MyTable);
% Uses backup Table to add variable names
% (the readtable above means the bad characters in variable names are already escaped!)
MyTable.Properties.VariableNames = MyTableBackup.Properties.VariableNames;
This means the new values exist as strings ('1', not 1 as a double), so now I just str2double when I access them for analysis. My takeaway - Matlab is for numbers. Thanks again all!
I have a 2d matrix (A=80,42), I am trying to split it into (80,1) 42 times and save it with a different name. i.e.
M_n1, M_n2, M_n3, … etc (representing the number of column)
I tried
for i= 1:42
M_n(i)=A(:,i)
end
it didn't work
How can I do that without overwrite the result and save each iteration in a file (.txt) ?
You can use eval
for ii = 1:size(A,2)
eval( sprintf( 'M_n%d = A(:,%d);', ii, ii ) );
% now you have M_n? var for you to process
end
However, the use of eval is not recommanded, you might be better off using cell array
M_n = mat2cell( A, [size(A,1)], ones( 1, size(A,2) ) );
Now you have M_n a cell array with 42 cells one for each column of A.
You can access the ii-th column by M_n{ii}
Generally, doing if you consider doing this kind of things: don't.
It does not scale up well, and having them in one array is usually far more convenient.
As long as the results have the same shape, you can use a standard array, if not you can put each result in a cell array eg. :
results = cell(nTests,1)
result{1} = runTest(inputs{1})
or even
results = cellfun(#runTest,inputs,'UniformOutput',false); % where inputs is a cell array
And so on.
If you do want to write the numbers to a file at each iteration, you could do it without the names with csvwrite or the like (since you're only talking about 80 numbers a time).
Another option is using matfile, which lets you write directly to a variable in a .mat file. Consult help matfile for the specifics.
Right now I am creating mapstructs in Matlab and then exporting them individually as shape files using the shapewrite() function.
However, instead of exporting them individually I want to store all of them into an array and then save it at the end as one single shapefile which holds all of the points from the mapstructs stored in the array.
My problem is I don't know how to initialize an array to hold these mapstructs. I've tried
`a = struct(sizeofarray)`
but it isn't compatible with mapstructs. I would appreciate any help!
You can store any kind of data in a cell array:
a = cell(sizeofarray,1);
You can then assign them like this:
a{1} = firstmapstruct;
a{2} = secondmapstruct;
However, if I understand you correctly you have mapstructs from the MATLAB Mapping Toolbox and want to concat structs of this form:
firstmapstruct =
609x1 struct array with fields:
Geometry
BoundingBox
X
Y
STREETNAME
RT_NUMBER
CLASS
ADMIN_TYPE
LENGTH
So you should probably do
a = firstmapstruct;
a(end+1:end+numel(secondmapstruct))= secondmapstruct;
and so on...
If all of your individual mapstructs have the same fields, you should be able to initialize a structure array by replicating one of your mapstructs using the function REPMAT:
a = repmat(mapstruct1,1,N); %# A 1-by-N structure array
Then just fill in each element as needed:
a(2) = mapstruct2; %# Assign another mapstruct to the second array element
a(3).X = ...; %# Assign a value to the X field of the third element
a(3).Y = ...; %# Assign a value to the Y field of the third element
You can find out more information about Geographic Data Structures in this documentation.
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