This question already has answers here:
Reading a text file in MATLAB line by line
(5 answers)
Closed 6 years ago.
let us suppose we have following table
% El-Centro earthquake signal:
% North-south component recorded at Imperial Valley Irrigation District
% substation in El Centro, California, during the Imperial Valley,
% California earthquake of May, 18, 1940. The magnitude is 7.1. and the maximum ground acceleration is 0.3495g
%
% Time (sec) Acceleration (g)
0.0000000e+00 1.1000000e-03
2.0000000e-02 1.1000000e-03
4.0000000e-02 1.3000000e-03
6.0000000e-02 1.4000000e-03
8.0000000e-02 1.3000000e-03
1.0000000e-01 1.2000000e-03
it is just fragment, i would like to create two dimensional table, one for time and second for acceleration,first of all we should skip text lines, i have tried following command
M = dlmread('ELCENTRO.txt', ' ', 6, 0);
that means i have skipped 6 row, but after i got matrix with dimension of
size(M)
ans =
2829 7
based on result i have done another command
M = dlmread('ELCENTRO.txt', ' ', 6, 3);
and now dimension of M changed
size(M)
ans =
2829 4
now i can do following thing
M(:,2:3)=[];
now M contains two column, one for time and second for signal, but how can i do this using dlmread command? thanks in advance
dmlread is a pretty old function with few bells and whistles. It appears that it won't work for your file as you have a 2 character delimiter (i.e. two spaces between the numbers).
But even if it did work, you're better off using tables for this type of data.
tbl = readtable('ELCENTRO.txt','HeaderLines',6,'ReadVariableNames',false,'Format','%f %f')
You then want to change the column names,
tbl.Properties.VariableNames = {'Time','Acceleration'}
In many cases the names could be read from the file, but the format of your file precludes that.
If you're not used to using tables then see the following as a starting point on how to manipulate them,
docsearch('Access Data in a Table')
In particular, if you do really just want the data as a matrix then do,
M = tbl{:,:}
Related
In a Windows 7 environment, I need to do a gnuplot scatter plot of 2 columns selecting data based on a range of values in a 3rd column. I know how to do it by creating separate data files for each range, but is it possible to do it by filtering on the data value in a 3rd column without awk
Thanks
plot "<awk '{if($3>=11 && $3<=19) print $0}' plot.dat " using 1:2 with points
warning: Skipping data file with no valid points
I Presume the error is because I don't have awk in windows7 envirenment
There are (should be) many examples of filtering data with gnuplot here on StackOverflow, however, mostly combined with another issue. So, whenever I'm trying to search for a really good and clear example, it takes more time for searching than to simply write down the line.
You definitely don't need awk!
Attention: Filtered data will not be connected in a line plot. So, in case you want to plot connected filtered lines, e.g. with lines or with linespoints you need to prepend an extra line. I assume you have gnuplot>=5.0.
For older gnuplot versions you can check this workaround.
The following will plot column 1 versus column 2, but only if column 3 is in the range 11 to 19.
set datafile missing NaN
plot "myData.dat" u 1:($3>=11 && $3<=19 ? $2: NaN) w linespoints
This question already has an answer here:
Summing up till a certain interval
(1 answer)
Closed 8 years ago.
I have a dataset (which is an hdf5 file) that contains a list of 250000 values, all quite small (sub 10). I want to cut this into 5000 pieces, so 50 each, and I want to individually sum the values in each of these 5000 pieces. I then want to create a histogram of these 5000 pieces, so I need to store them as well.
I am trying to do this using MATLAB, as my very limited programming skills have been developed using this, and it seems suitable for these purposes. Now, I haven't gotten very far, but what I have done so far is:
for n = 1:50:249951
% CR check before (before pumping?)
ROdata = h5read('hdf5file', '/data', [n], [n+49]);
sum(ROdata)
end
Of course, this does not yet store the values of the sum for each n. But more importantly, it does not work. For n = 1, all is fine, and I get the correct value. But already for n = 51, (so summing 51-100), I do not get the correct sum. What's going wrong here?
How should I store these (not working) sums?
Are you looking for something like this?
I assumed you already read your data and you have a 250000x1 vector.
%example data
data = randi(42,1,250000);
% rearranges your vector in groups of 50
A = reshape(data,[],5000);
% sums every column of your reshaped vector
sums = sum(A,1);
hist(sums,5000)
I have results which are 6 columns long however have been printed as 2 then 3 beneath then 1 beneath that! There are hundreds of lines and matlab will not except the structure of the matrix as it is now. Is there any way to tell matlab i want the first 5 results in their own columns then continuing down the rows after that?
My results appear as follows:
0.5 0
0.59095535915335684063 -0.59095535915335395405 -5.89791913085569763
33e-08
... repeated alot
thansk so much, em xx
I would just do a format shortE before you process the output, this will give you everything in scientific notation with 4 digits after the decimal. That 'should' allow you to fit your columns all in one line, so you don't have to deal with the botched output.
In general you should not want the output to be in a too specific format, but suppose you have this matrix:
M =[0.5 0 0.59095535915335684063 -0.59095535915335395405 -5.89791913085569763 33e-08];
To make it an actual matrix I will repeat it a bit:
M = repmat(M,10,1);
Now you can ensure that all six columns will fit on a normal screen by using the format.
format short
Try help format to find more options. Now simply showing the matrix will put all columns next to eachother. If you want one column below, the trick is to reduce your windows width untill it can only hold five columns. Matlab will now print the last column below the first.
M % Simply show the matrix
% Now reduce your window size
M % Simply show it again
This should help you display the numbers in matlab, if you want to process them further you can consider to write them to a file instead. Try help xlswrite for a simple solution.
Could somebody explain the following code snippet? I have no background in computer science or programming and just recently became aware of Matlab. I understand the preallocation part from data=ceil(rand(7,5)*10)... to ...N*(N-1)/2).
I need to understand every aspect of how matlab processes the code from kk=0 to the end. Also, the reasons why the code is codified in that manner. There's no need to explain the function of: bsxfun(#minus), just how it operates in the scheme of the code.
data=ceil(rand(7,5)*10);
N = size(data,2);
b=cell(N-1,1);
c=NaN(size(data,1),N*(N-1)/2);
kk=0;
for ii=1:N-1
b{ii} = bsxfun(#minus,data(:,ii),data(:,ii+1:end));
c(:,kk+(1:N-ii)) = bsxfun(#minus,data(:,ii),data(:,ii+1:end));
kk=kk+N-ii;
end
Start at zero
kk=0;
Loop with ii going from 1 up to N-1 incrementing by 1 every iteration. Type 1:10 in the command line of matlab and you'll see that it outputs 1 2 3 4 5 6 7 8 9 10. Thuis colon operator is a very important operator to understand in matlab.
for ii=1:N-1
b{ii} = ... this just stores a matrix in the next element of the cell vector b. Cell arrays can hold anything in each of their elements, this is necessary as in this case each iteration is creating a matrix with one fewer column than the previous iteration.
data(:,ii) --> just get the iith column of the matrix data (: means get all the rows)
data(:, ii + 1:end) means get a subset of the matrix data consisting of all the rows but only of columns that appear after column ii
bsxfun(#minus, data(:,ii), data(:,ii+1:end)) --> for each column in the matrix data(:, ii+1:end), subtract the single column data(:,ii)
b{ii} = bsxfun(#minus,data(:,ii),data(:,ii+1:end));
%This does the same thing as the line above but instead of storing the resulting matrix of the loop in a separate cell of a cell array, this is appending the original array with the new matrix. Note that the new matrix will have the same number of rows each time but one fewer column, so this appends as new columns.
%c(:,kk + (1:N-ii)) = .... --> So 1:(N-ii) produces the numbers 1 up to the number of columns in the result of this iteration. In matlab, you can index an array using another array. So for example try this in the command line of matlab: a = [0 0 0 0 0]; a([1 3 5]) = 1. The result you should see is a = 1 0 1 0 1. but you can also extend a matrix like this so for example now type a(6) = 2. The result: a = 1 0 1 0 1 2. So by using c(:, 1:N-ii) we are indexing all the rows of c and also the right number of columns (in order). Adding the kk is just offsetting it so that we do not overwrite our previous results.
c(:,kk+(1:N-ii)) = bsxfun(#minus,data(:,ii),data(:,ii+1:end));
Now we just increment kk by the number of new columns we added so that in the next iteration, c is appended at the end.
kk=kk+N-ii;
end;
I suggest that you put a breakpoint in this code and step through it line by line and look at how the variables change in matlab. To do this click on the little dashed line next to k=0; in the mfile, you will see a red dot appear there, and then run the code. The code will only execute as far as the dot, you are now in debug mode. If you hover over a variable in debug mode matlab will show its contents in a tool tip. For a really big variable check it out in the workspace. Now step through the code line by line and use my explanations above to make sure you understand how each line is changing each variable. For more complex lines like b{ii} = bsxfun(#minus,data(:,ii),data(:,ii+1:end)); you should highlight code snippets and ruin these in the command line to see what each part is doing so for example run data(:,ii) to see what that does and then try data(:,ii+1:end)) or even just ii+1:end (well in that case it wont work, replace end with size(data, 2)). Debugging is the best way to understand code that confuses you.
bsxfun(#minus,A,B)
is almost the same as
A-B
The difference is that the bsxfun version will handle inputs of different size: In each dimension (“direction,” if you find it easier to think about that way), if one of the inputs is scalar and the other one a vector, the scalar one will simply be repeated sufficiently often.
http://www.mathworks.com/help/techdoc/ref/bsxfun.html
i am trying this code since last night but i cant understand what this code is doing. actually i am beginner in matlab programming
load('79.mat')
trainingData=d79;
colormap(gray);
colormap(grey);
x=reshape(d79(1234,:),28,28);
y = x(:,28:-1:1);
pcolor(y');
Kindly help me in understanding this code. :/
This is pretty simple. Here is a line-by-line explanation:
Loads data from a data file
Puts the loaded data into a variable named trainingData
Sets the colormap for plotting
Take the 1234th row of the loaded matrix, convert it into a 28-by-28 matrix, and store it in the variable x. So for example, on a smaller scale, [5 6 7 8] is converted to the matrix [5 7; 6 8] if you want to reshape that matrix to 2-by-2.
Reverse the column order of x and put that in y. So the last column becomes the first, second-last becomes second, etc.
This is a checkerboard plot of the values contained in y.
Edited to include more detail on lines 5 and 6:
The reshape line assumes that there is a row with number 1234, and that there are 784 (28*28) elements in that row. It takes that row, and makes a 28x28 matrix out of it, by taking the first 28 elements, making them into the first column of the new matrix, then taking the next 28 elements, making them the second column, and so on 26 more times. The final matrix is names x.
For the y line, like I said, it just reverses the columns of x, it puts the last column first, the second-last column second, and so on until the first column of the x is put as the last column of y.