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How do I plot vectors of different length on the same axes in MATLAB?

Answer 1

+1 A:

I assume you are first reading data from the files as described in the answers to this question. If you have the time-stamps (converted using DATENUM) and data from the two files stored in variables fileData1 and fileData2, the following is a simple way to plot data from each on the same set of axes (using the function PLOT and the HOLD command):

t1 = fileData1(:,1);  %# Time-stamps for file 1
d1 = fileData1(:,2);  %# First column of data for file 1
plot(t1,d1,'ro-');    %# Plot data from file 1, using a red line with circles
hold on;
t2 = fileData2(:,1);  %# Time-stamps for file 2
d2 = fileData2(:,2);  %# First column of data for file 2
plot(t2,d2,'bo-');    %# Plot data from file 2, using a blue line with circles

Each line in the above plot will have a different number of time points (i.e. circle markers), but each will be a continuous (i.e. unbroken) line. If you want to show breaks in the plot where there are missing time-stamps, you can pad the data from file 1 with NaN values. If you know for sure that there are never time-stamps in the smaller file that aren't in the larger file (i.e. that the time-stamps in the smaller file are a subset of the time-stamps in the larger), then you can use the function ISMEMBER as follows:

newData = nan(size(fileData2));      %# New file 1 data, initialized to NaN
t = fileData2(:,1);                  %# Use the time-stamps from file 1
index = ismember(t,fileData1(:,1));  %# Find row indices of common time-stamps
newData(:,1) = t;                    %# Copy time-stamps
newData(index,:) = fileData1;        %# Copy data

If there are time-stamps in the smaller file that aren't in the larger, then you will have to use a solution based on the INTERSECT function (as illustrated in my answer to your other related question).

And now, you can plot the data using the following:

d1 = newData(:,2);            %# First column of padded data for file 1
d2 = fileData2(:,2);          %# First column of data for file 2
plot(t,d1,'ro-',t,d2,'bo-');  %# Plot both lines

Here's a sample of the difference NaN-padding makes when plotting (using some randomly generated data):

alt text

gnovice 2009-11-18 02:18:01

Thanks a lot, As you had seen from my other question that you commented too , i spend tons of time to figure the above problem.

AP 2009-11-18 04:27:04

@gnoice : is there a way to plot a matrix which is in cell format? normally i use > plot(x,y) x= data(:,1); y=data(:,2); how do i do the same when data is in cell? i tried cellplot, did not work. Also tried x=cell2mat(data(:,1)) ; did not work either.

AP 2010-03-19 18:53:13

@AP: That depends on what your variable `data` looks like. Is it an N-by-2 cell array with one number per cell? Or is it a 1-by-2 cell array where each cell contains an N-by-1 vector? The first case can be handled like this: `plot([data{:,1}],[data{:,2}]);` And the second case can be handled like this: `plot(data{1},data{2});` Without more detail about what `data` looks like, that's the best I can answer.

gnovice 2010-03-19 19:32:10

@gnoice: Its a N,M matrix, I make it work by writing a xlsfile and rereading it as data=xlswrite(' ') ; This seems like a round about way of doing it. With either of the two commands it gave the same error ' invalid first data argument '

AP 2010-03-19 19:57:37

@AP: Do you mean to say `data = xlsread(...);`? Using XLSWRITE will just return a logical flag for the value of `data` indicating whether the write operation was successful. If you use `data = xlsread(...);`, your matrix `data` will be a numeric array, not a cell array, so you should be able to plot it with `plot(data(:,1),data(:,2))`.

gnovice 2010-03-19 20:30:56

@gnoice: Sorry if i confused you. I know i can plot the way you mentioned. Ok here is what i am doing. I have a file of size (20 20) and its in cell as i have processed and did many operations on it. now in the end i am writing a xlsfile... using xlswrite ('newfile.xls', file);NOW i wanna plot column 1 Vs Column 2 of file.is there anyway of not doing agiandata= xlsread ('newfile.xls')and then plotting?is there a way to convert my cell format to num so i can plot directly from file?

AP 2010-03-19 20:38:14

@AP: Ahhhh, I've got it now. The problem is likely that you have strings in the top row of your cell array `file`. Those strings are causing the error you were getting. You have to pick only those cells with numeric values in them for the plotting. If your strings are only in the top row of `file`, this should work: `plot([file{2:end,1}],[file{2:end,2}]);`

gnovice 2010-03-19 20:51:32

@gnoice: Yes you are right yet agian :P. I had empty strings on the first row and last 5 rows and so i had the problem. I guess there is no way to delete the empty rows i used file = file(~any(cellfun(@isempty,file),2),:); but did not work

AP 2010-03-19 21:22:18

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How do I plot vectors of different length on the same axes in MATLAB?

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