Numerical Matrix CSV -> Covariance Matrix - matlab

I have a CSV file containing a numerical matrix with over two thousand New York Stock Exchange listed companies' value over two years.
It seems like it should be really simple - I want to attain a covariance matrix formed from the CSV matrix.
As far as I'm aware I simply need to:
Import the data as numerical matrix (just the data no headings etc) using the MATLAB Import Data button.
Press save as on the workspace variable and make e.g. NYSE.mat.
In my function call cov(NYSE.mat);
This should access the matrix and return a large covariance matrix from my data. The cov() function works when i manually input an example matrix of for example:
[5 0 3 7; 1 -5 7 3; 4 9 8 10];
But for some reason whenever I try to call cov(NYSE.mat); only one number is returned, rather than a covariance matrix.
Can anyone tell me where I'm going wrong? I've been trying to figure this out for a while now and I feel the answer should be really simple.
I'm running on MATLAB R2016a.

Not sure you need to manually save the workspace name in step 2. As part of your import process you once you click the import button the variable should be loaded into workspace with the name of the file (maybe NYSE)
Try Load('NYSE.mat') and see what appears in your workspace.
Once you figure out the name of the variable, calling the function with that.

If your CSV file is without any header lines (not sure if any CSV file needs them) and contains only numbers, you can simply call
x = importdata('<nameofyourcsv>.csv');
and then
c = cov(x);
or even do it in one step:
c = cov(importdata('nameofcsv.csv'));
This function is equivalent of clicking on the button you mention. However, if your file contains header lines, you have to specify its number and call this function with more parameters:
x = importdata('nameofcsv.csv',',', nh); % nh is a number of header lines
x will no longer be a regular MATLAB matrix but a structure with following fields: data, textdata, and colheaders. cov(x.data) will calculate covariance. Not sure why you would need to save anything in a mat file, though. If you wish, you would probably need to assign a value from a data field to a regular variable and then save such variable. Otherwise, you will save the whole x structure.
For instance, the following file, test.csv:
95.01,76.21,61.54,40.57,5.79,20.28,1.53
23.11,45.65,79.19,93.55,35.29,19.87,74.68
60.68,1.85,92.18,91.69,81.32,60.38,44.51
48.60,82.14,73.82,41.03,0.99,27.22,93.18
89.13,44.47,17.63,89.36,13.89,19.88,46.60
can be imported by calling importdata:
>> x = importdata('test.csv')
x =
95.0100 76.2100 61.5400 40.5700 5.7900 20.2800 1.5300
23.1100 45.6500 79.1900 93.5500 35.2900 19.8700 74.6800
60.6800 1.8500 92.1800 91.6900 81.3200 60.3800 44.5100
48.6000 82.1400 73.8200 41.0300 0.9900 27.2200 93.1800
89.1300 44.4700 17.6300 89.3600 13.8900 19.8800 46.6000
EDIT
I downloaded the file and copy pasted this command from your answer:
c = importdata('nyse_data_matrix_no_tags.csv');
Then, I opened the file in a text editor and copied 1st and 20th row of numbers in the file and created a matrix in MATLAB:
x = [46.09,24.69,156.78,5.95,21.14,76.17,55.51,7.04,38.87,19.58,47.57,7.73,119.44,1.61,44.55,24.9,50.89,4.87,26.25,15.95,15.96,39.14,121.27,15.7,25.91,25.8,69.7,16.32,12.86,7.89,247.4,27.11,41.6,5.14,47.77,40.98,13.78,26.058,14.56,41.05,24.27,47.13,40.92,27,85.04,15.06,5.05,29.14,7.51,67.5,67.79,42.68,124.86,24.28,27.82,18.08,100.67,109.07,12.59,50.34,18.64,4.75,6.06,16.63,109.86,14.1,54.48,13.9,59.98,16.24,45.53,4.06,67.99,18.22,4.2,117.23,158.75,5.7,2.46,76.39,77.79,6.17,16.95,5.27,12.74,14.7,19.14,14.4,42.77,26.4,14.17,76.57,12.4,42.07,77.47,41.27,60.53,16.97,65.71,56.13,258.4,28.96,760.07,60.46,34.77,133.1,14.19,29.41,11.78,154.55,44.75,15.18,17.52,24.86,36.18,14.1,30.1,47.65,22.92,47.37,61.84,226.52,10.2,65.14,7.88,16.34,170.23,9.6,34.42,15.0999,20.34,58.7,16.6,14.72,14.32,20.89,14.32,13.2,6.05,422.96,21.43,47.55,13.28,27.98,8.16,45.15,15.1665,41.65,17.45,25.73,63.03,16.07,17.56,11.54,6.54,33.18,15.01,357.96,74.88,15.24,27.24,69.08,36.29,76.55,65.72,50.93,72.73,16.13,23.81,52.14,16.05,12.19,71.77,14.97,11.82,33.04,7.86,15.26,72.46,15.42,24.49,15.75,63.78,32.43,36.57,16.24,7.08,26.08,15.74,14.78,16.22,16.85,23.32,31.14,12.72,6.7,26.65,24,12.95,129.92,20.07,11.28,34.66,12.86,17.5,26.5,0.7038,1.22,128.98,23.33,19.2,15.64,8.34,45.01,38.14,50.31,13.11,17.4,47.15,79.29,8.24,28.92,24.97,1.92,77.16,126.5,8.97,3.97,12.85,30.75,37.82,2.36,10.37,52.28,1.56,53,47.33,41.32,10.65,15.24,39.5,94.42,12,54.25,48.03,3.72,6.34,18.5,23.47,26.74,8.74,6.7,7.08,70.92,27.3,65.43,18.776,7.82,16.8,12.0625,124.24,29.79,22.88,29.4,66.44,28.88,1.505,0.8642,10.37,47.14,99.83,133.87,46.41,4.88,57.63,14.45,11.2,34.99,11.06,129.25,7.71,35.2,2.29,2.53,1.65,13.74,15.6,11.84,59.79,33.85,62.48,72.34,25.15,131.2,61.13,2.17,5.1,53.35,26.9,43.15,10.8,63.61,130.91,81.42,45.29,17.58,415.79,118.64,73.88,9.85,79.22,43.39,4.86,32.18,68.36,60.21,34.15,19.47,23.39,29.96,39.58,14.66,5.98,70.87,25.9,38.64,90.45,165.2,46.57,83.18,16.48,134.15,54.68,62.51,12.25,24.33,17.69,60.73,11.51,15.6,85.99,80.81,59.9,17.48,30.73,104.34,0.94,86.03,82.73,14.41,34.05,17.2,11.98,13,52.5,39.2,19.58,101.59,26.38,44.13,18.72,23.3,32.05,27,26.12,13.13,18.58,6.07,73.74,3.53,42.4,12.21,15.72,16.71,26.27,26.69,4.52,35.99,26.1,17.31,45.61,67.9,11.15,13.08,1.1,9.7001,17.51,59.8,26.27,86.95,18.95,26.75,34.33,66.72,107.98,9.7,18.27,24.16,56.8,46.56,91.69,21.43,78.75,3.37,13.71,31.73,100.39,5.65,6.98,85.21,97.84,13.5,26.19,42.43,26.73,10.11,47.95,102.84,66.95,28.35,14.07,5.25,23.68,127.43,11.41,10.43,4.19,25.48,19.78,72.08,53.59,17.41,36.57,92.37,127.48,23.98,16.46,5.28,24.76,9.1,68.33,64.45,8.15,18.54,8.85,119.72,3.62,20.49,2.57,94.05,16.99,25.93,25.12,25.71,9.68,81.26,16.7,77.21,37.45,80.43,6.95,24.95,87.1,20.74,31.82,25.44,25.48,25.5515,46.96,19.11,43.49,10,8.68,16.99,120.79,3.95,1.91,76.54,7.8,33.71,14.59,13.5,15.99,42.6,38.86,46.76,8.1,23.14,23.04,17.39,15.4399,13.62,14,125.94,13.92,22.98,48.68,4.62,68.17,1.14,9.82,29.75,73.66,6.51,92.28,25.53,25.6,25.63,7.59,72.9,25.23,10.41,27.87,10.81,48.76,11.38,3.76,71.78,13.21,53.59,25.55,42.43,68.21,66.25,37.2,6.1,6.24,84.58,13.17,13.2,22.92,82.95,28.9,6.07,74.57,29.35,74.89,64.46,77.91,30.21,11.09,6.34,21.69,56.88,15.25,41.44,1.77,67.42,209.26,11.24,15.8,13.53,15.09,32.8,9.78,12.99,62.77,21.8,39.11,78.68,14.75,10.67,20.6,10.57,36.39,7.24,6.1,13.61,14.58,51.04,20.36,102.48,35.14,12.31,8.98,3.7,81.22,89.67,27.32,13.26,1.54,37.84,11.29,8.98,24.08,4.43,8.54,15.51,36.26,9.33,6.56,43.38,13.04,10.9,54.68,160,164.11,34.25,15.87,14.65,18.72,10.57,13.25,21.08,62.55,6.08,22.72,17.25,14.1,11.91,16.5,17.36,4.93,31.46,75.14,32.84,55.65,21.39,18.76,53.36,52.27,150,11.51,50.35,4.77,16.2,13.83,43.24,94.4,37.89,13.18,35.9,70.65,14.16,11.8273,12.67,22.93,11.11,13.55,9.55,14.24,26.44,13.49,69.92,9.88,157.12,14.93,6.53,13.5,6.83,28.27,13.07,48.33,59,9.67,2.04,28.2,5.82,31.87,65.9,33.14,36.14,30.08,8.49,64.92,4.76,141.98,8.63,10.11,17.27,19.65,30.24,26.53,40.67,26.87,26.25,39.18,1.54,33.93,16.59,7.33,15.36,13.91,1.1,17.12,4.47,15.67,18.68,1.79,15.54,81.13,21.34,27.59,7.46,10.77,503.01,19.74,18.46,15.26,47.57,30.24,6.55,65.34,4.13,13.2,21.55,21.03,29.36,27.27,47.72,10,26.17,7.45,7.62,3.48,18.15,8.2,20.66,97.23,59.46,13.37,7.8,76.6,19.31,9.21,24.18,77.53,0.9,10.8,153.17,23.32,1.18,25.83,42.06,1.48,11.49,24.78,18.24,21.24,6.59,44.54,33.28,64.61,227.17,30,48.14,29.72,45.5,79.45,26.83,4.96,81.03,30.76,72.15,34.48,129.3,65.48,33.48,67.43,34.31,15.05,60.38,32.59,26.84,1.7,32.48,2.31,113.96,1.13,7.3,31.13,12.27,44.48,163.75,4.55,4.93,49.64,7,0.42,4.66,62.44,41.56,21.6,8.18,26.89,33.78,3.79,47.23,27.86,0.5199,45.15,117.21,9.51,74.52,1.8,67.24,22.28,22.735,28.48,13.84,19.61,26.62,25.78,18.95,33.53,21.54,51.22,13.79,34.9,81.22,6.86,15.59,96.42,18.49,31.21,24.57,21.23,22.93,16.32,10.63,11.18,188.35,16.08,18.39,18.17,43.96,62.54,8.82,1.87,33.38,14.9,10.47,16.69,3.2,8.89,3.95,50.02,153.42,7.65,35.53,0.54,18.36,5.24,262.52,4.07,74.98,12.53,13.66,86.82,129.8,24.78,9.8,7.03,21.68,8.1,17.1,7.5,38.4,118.45,6.47,26.92,17.2,7.6,35.32,1.72,25.83,9.11,26.27,13,12.18,12.29,44.75,26.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.3,112.64,26.1,44.12,5.27,8.25,22.99,68.65,75.61,9.07,53.28,10.89,87.69,7.53,5.49,28.77,16.93,31.76,56.22,26.5,25.85,25.7401,6.03,8.52,73.39,17.69,37.86,20.07,20.07,38.7,29.07,148.17,37.66,43.78,7.71,8.06,21.2,15.01,7.65,36.81,27.64,25.07,37.7,41.81,20.87,133.29,56.32,7.4,45.66,1.77,9.84,44.71,111.33,129.74,33.85,83.84,12.96,101.79,60.87,4.87,41.94,27.98,38.29,20.16,3.28,39.63,101.46,18.22,55.85,25.52,26.35,77.89,58.71,106.91,106.8875,82.26,18.76,74.11,14.07,22.74,9.85,32.93,60.84,3.9,14.49,14.35,21.27,1.82,12.3,13.61,54.78,46.51,13.6,9.1,116.12,134.97,14.18,56.62,96.69,3.28,13.6,14.19,47.52,24.93,12.36,27.7,10.77,15.9,66.72,50.39,30.56,4.05,51.47,27.54,37.84,79.17,4.41,34.21,134.96,105.34,35.36,55.08,92.92,69.47039835,24.05,19.76,12.71,60.18,48.91,90.11,26.55,49.2,5.82,2.9,68.28,20.82,40.56,56.32,171.54,11.4,11.94,10.99,11.91,13.69,45.01,10.93,61.78,19.05,9.11,46.67,23.65,66.85,14.14,21.6,30.4,35.89,63.93,10.56,14.96,9.02,29.15,52.18,56.31,29.22,38.54,54.51,133.93,13.7,71.27,2.27,825.61,32.84,56.14,13.07,19.25,17.79,17.89,31.23,69.13,14.81,1.75,115.34,41.85,4.97,33.71,89.67,24.5,27.18,5.98,53.57,9.24,43.24,526.42,3.48,20.92,81.57,5.13,117.44,23.66,12.76,14.3,32.23,12.09,46.25,4.9,5.77,6.24,11.94,8.45,6,38.21,2.05,1.18,1.19,2.17,0.73,3.23,3.05,1.46,2.06,4.68,18.27,0.3199,31.48,2.59,16.44,16.85,16.9,11.91,1.74,122.34,0.82,3.33,0.55,13.02,19.46,2.6,55.43,18.83,28.86,34.75,11.76,10.8,9.5,48.62,12.54,12.8,16.6,16.22,2.9,2.33,16.09,14.56,0.5024,0.24,9.84,0.15,13.19,13.82,14.1466,13.15,13.88,14.07,13.68,14.38,14.85,7.69,0.7663,0.324,1.89,5.35,0.9,0.77,23.7,1.2863,11.39,11.24,6.43,0.97,4.2127,0.3302,2.21,3.5,1.54,0.6,2.65,27.28,2.75,1.78,9.52,2.35,0.11,0.1212,5.68,13.86,31.34,7.6,0.42,1.56,0.6299,12.7,1.05,0.94,2.37,17.12,3.66,0.21,12.61,13.18,1.52,0.3221,0.6634,10.9,63.43,16.37,10.54,16.52,7.5,14.62,5.24,2,3.53,4.53,0.3581,4.75,2.59,0.7299,6.13,0.165,16.42,15.63,9.37,15.04,14.15,10.95,31.46,17.57,6.71,0.525,89.54,0.225,2.27,15.71,2.89,0.84,0.79,30.57,0.2603,8.49,7.26,19.76,44.32,0.6701,2930.11,0.51,2.29,12.6,2.07,0.49,0.5058,1.06,17.75,0.3579,63.51,0.8301,0.75,0.78,0.4875,0.7495,2.52,4.35,0.82,7.66,12.36,12.96,10.735];
I compared matrix x with the 1st and 20th row of c and they are equal:
isequal(x,c([1 20],:))
ans =
1
importdata seems to be working as expected.

Related

How to read rows from a text file into an array?

I have a program which finds linear fitting, now I want to provide x elements from text file , y elements will remain the same , I want b(2) as a output for all 128 rows , which will be taken as input from trial2.txt
I want to read 128 rows which contains 3 columns, one by one and put those into x0[], then find b(2)
x0=[];
y0=[5.15659,5.48556,5.80477];
X1 = [ones(length(x0),1) x0'];
b = X1\y0';
plot(x0,y0,'o')
y = b(1) + x0*b(2)
hold on
plot(x0,y,'--r')
fid=fopen('data.txt','a+');
fprintf(fid,'%10.1f %10.4f %10.4f %10.9f\n',x0,b(2));
fclose(fid);
The best way to get started with importing data into MATLAB is to use the interactive "Import Tool". If you like the way it imports your data, you can get it to generate some re-usable MATLAB code so that you don't need to the use the UI next time round.

Efficiency loading a file into Matlab

I am trying to load a file in Matlab. But I am a bit confused about the best way to do it.
The file has 3 columns and looks like the screenshot below:
This file I can load very quickly by doing load('c').
However, I had to add 2 NaNs on the bottom row.
The original file actually looks like the file below:
Now if I do load('c') on the file below I get the error:
Error using load
Unable to read file 'c'. Input must be a MAT-file or an ASCII file containing numeric
data with same number of columns in each row.
Of course I can use ImportData to import this file, but it is just soooo slow to import it.
Any suggestions?
You should be able to use c = readtable('c'). This should automatically change the empty entries to "NaN" by default, but if not, there is a way to set that in the options.
If I have a file that is tricky to import (prior to readtable()...that made things a lot easier in the last few years), I will often use the Import Data tool (if its a really big file you can make a mock-up of the complicated file so it loads faster) then change all the import settings as I would want it, then where the green check says "Import Selection" use the black drop down arrow to select "Generate Function." This will give you the coded way of setting everything up to get the file in just the way you want it.
load() is better suited for reading in previously saved '.mat' files that were created in Matlab.
Here's a low-level approach, which might be faster than other methods:
filename = 'c'; % name of the file
N = 3; % number of columns
fid = fopen(filename, 'r'); % open file for reading
x = fscanf(fid, '%f'); % read all values as a column vector
fclose(fid); % close file
x = [x; NaN(N-mod(numel(x)-1,N)-1, 1)]; % include NaN's to make length a multiple of N
x = reshape(x, N, []).'; % reshape to N columns in row-major order

Import multiple text files onto Matlab to analyze the data [duplicate]

This question already exists:
Generating vectors from multiple matrices
Closed 6 years ago.
I am really new in matlab. So i am trying to learn the very basics. I have 8 tsv files with names like 2004.07.01.0000.tsv, 2004.07.01.0300.tsv, where each file has 72 rows and 144 columns. I am trying to automatically import all of those files to matlab in a matrix form to calculate the mean, median, skewness (for data correction). What I did is that I imported one file (2004.07.01.0000.tsv) using matlab gui, then I generated a function called importfile. I am trying to use a for loop to access all the data in those files but I could not figure it out. I tried (not sure at all):
for fileNum=1:8;
startRow=1;
endRow=72;
filename
a=importfile(filename, startRow, endRow);
end
If your importfile() function works correctly, in this manner at every for-loop iteration you'll overwrite a with the most recent imported file. You should concatenate all your files (i.e. matrices) instead.
A matrix concatenation can either be done by rows (i.e. horizontal concatenation) or by columns (i.e. vertical concatenation). As I understand, you want a vertical concatenation in order to generate a unique matrix with 144 columns and as many rows as your single files contain.
Thus you should change the loop as follows
myMatrix=[];
for fileNum=1:8;
startRow=1;
endRow=72;
filename
myMatrix=[myMatrix ; importfile(filename, startRow, endRow)];
end
The vertical concatenation can be done by means of the ; operator, thus an instruction like A=[B ; C] will create a matrix A by concatenating matrices B and C. In your case you initialize myMatrix as empty and then you will vertically concatenate (in an iterative fashion) all outputs from importfile(), that are your .tsv files.
At the end of the loop, myMatrix should have size NxM where M is 144 and N is the sum of the number of rows across all your files (8*72).
Update
If you have to pass explicitly the filename to the importfile() function you can create a cell array of strings in which each element of the cell is a filename. Thus in our case the cell array will be something like:
filenames={'filename1.tsv','filename2.tsv',...,'filename8.tsv'};
obviously you must replace the strings inside the cell with the proper filenames and finally you can slightly edit the loop as follows
myMatrix=[];
for fileNum=1:8;
startRow=1;
endRow=72;
myMatrix=[myMatrix ; importfile(filenames{i}, startRow, endRow)];
end
In this manner, at every loop iteration the i-th filename will be given as input to importfile() and hopefully it'll be loaded.
For this to work you should (let's make things simple)
place your Matlab script and obviously the function importfile() in the same folder containing your .tsv files
set said folder as the Current Folder
or if you have the .tsv files in a given folder and your scripts in another folder, then the Current Folder must certainly will be the folder containing your scripts and the filenames inside the cell array filenames must contain the entire path, not just the proper filenames.

Getting the format correct when writing data to a text file from a matlab script

I'm trying to write data to a text file from my matlab script. I want two columns which it gives me but I want my time variable (t) followed by my variable (x) which is my amplitude. Its outputting a file like below.
Everything is perfect however i don't believe my (t) variable is first followed by my (x) variable. I'm trying to upload this file to ploy.ly to be graphed but when i set column 1 to my x variable and column 2 to my y variable it plots a oval like below. It's suppose to plot a sinusoidal signal.
My code is as follows:
f = 1E3;
T = 1/f;
tmin = 0;
tmax = 5*T;
dt = T/100;
t = tmin:dt:tmax;
x = sin(2*pi*f*t);
sinData.txt = fopen('sinData.txt','w');
fprintf(sample.txt,'%7.5f,%7.5f\r\n',x);
fclose(sinData.txt);
plot(t,x,'r');
grid on;
MATLAB writes files in column major format. What this means is that it will traverse every row first in one column before moving to the next column. If you have a M x 2 matrix of values where the first column is a vector of t values and the second column is a vector of x values, try transposing the matrix before writing to file. That way, each column represents a pair of (t,x) values for you and MATLAB should be able to preserve writing to the file so that each row is a unique pair.
Also, in your code you are only writing the x values to the file. This makes sense because if you look at your text file going line by line, it pretty much mimics a sinusoidal output. It goes from 0 up to 1, then back to 0 again. Your x vector is a sinusoidal output which thus fits the pattern. As such, you probably want to write the t values as well. To do this, modify the fprintf statement in your code so that it looks like this:
fprintf(sinData.txt,'%7.5f,%7.5f\r\n', [t;x]);
BUG SPOT FROM RTL (Thanks!): Make sure you change sample.txt to sinData.txt in your fprintf statement as that is the name of the handle to the open file that you have opened.
Looking at your code, t and x are row vectors, so this should (hopefully) work. I haven't tried it myself, and I'm somewhere where I don't have MATLAB accessible. Hit me up with a comment and let me know if it works.

How to save data using matfile Matlab

New to matlab and I need some help.
I need to create a .mat file , using matObj or save(), that has some information that will be passed from some variable. Lets say that variable x = 1,2,3,4,5
1|2|3|4|5|
Then I need to save that in test.mat
Then I need to load that file and save something like,
6|7|8|9|10|
So I get
1|2|3|4|5|
6|7|8|9|10|
and so on.
So every time I save it goes to a new row. The numbers that go inside they are not random the above numbers are just there to make things simple to see.
Can someone help me out.
You are describing two different problems here. The first is saving and loading of data.
Saving is easy:
x = 1:5;
filename = 'myFile.mat'
save(filename, 'x'); %notice that I used the string name of the variable
Likewise loading is also simple:
filename = 'myFile.mat';
data = load(filename); % loaded variables are placed in a struct to prevent overwriting workspace variables
x = data.x;
The 2nd problem can be solved using concatenation:
lets say you want to convert the vector 1 2 3 into the matrix:
1 2 3
1 2 3
You can simply call:
v = 1:3;
m = cat(1, v, v);
Likewise you can add an additional row to the existing matrix using the same command:
m = cat(1, m, v);
I'm sure any amount of googling will get you how to save a variable to a mat file - The matlab docs are absolutely spectacular, and such a simple operation will be covered along with examples showing exactly how to use the functions.
As for the second part, use the concatenation property
new = [old1 old2];
to concatenate horizontally, and
new = [old1;old2];
to concatenate vertically. Then resave the same way that you just learned via google.
Hope this helps, and in the future, i guarantee 99% of the answers to a new user's questions will be in the top two google search results if you append "matlab" to your search. The Mathworks really set the bar on documentation in my opinion. (Of course, I last used MATLAB 3 years ago)