how to read only last 2 columns of csv format file?

i have to read last 2 columns and thwn write in a+bi format

b1 column data is continoiusly repeating 1-5 with n no of data and plot graph

x axis =b1 column

y axis =a+bi

2018 a version

Answer 1

[dpb]

data=readtable(websave('plot.csv','https://www.mathworks.com/matlabcentral/answers/uploaded_files/1147855/plot.csv'),'readvariablenames',1);
tXY=table(data.b1,complex(data.b2,data.C1),'variablenames',{'X','Y'})

tXY = 10×2 table
    X        Y    
    _    _________

    1    -4.2-5.2i
    2    -3.2+6.2i
    3    -5.2+3.2i
    4    -3.2-5.2i
    5    -6.2-6.3i
    1    -2.3-9.2i
    2     2.3-6.2i
    3     2.3-3.2i
    4     6.2-6.3i
    5     3.2-7.8i

But, MATLAB can't plot complex variables versus a real index as a line plot; it isn't clear what you have i mind here???

Answer 2

[Image Analyst]

Try this:

filename='plot.csv';
data= readtable(filename)

data = 10×5 table
    a1    a2    b1     b2      C1 
    __    __    __    ____    ____

     1    0     1     -4.2    -5.2
     2    0     2     -3.2     6.2
     3    0     3     -5.2     3.2
     4    0     4     -3.2    -5.2
     5    0     5     -6.2    -6.3
     6    0     1     -2.3    -9.2
     7    0     2      2.3    -6.2
     8    0     3      2.3    -3.2
     9    0     4      6.2    -6.3
    10    0     5      3.2    -7.8

x = data.b1

x = 10×1

1 2 3 4 5 1 2 3 4 5

% Get real component from column 4.
realValues = data{:,end-1};
% Get imaginary component from column 5.
imaginaryValues = data{:,end};
complexValues = realValues + 1i * imaginaryValues

complexValues = 
  -4.2000 - 5.2000i
  -3.2000 + 6.2000i
  -5.2000 + 3.2000i
  -3.2000 - 5.2000i
  -6.2000 - 6.3000i
  -2.3000 - 9.2000i
   2.3000 - 6.2000i
   2.3000 - 3.2000i
   6.2000 - 6.3000i
   3.2000 - 7.8000i

[riki singh]

Sir readtable is nt present in 2018a version

is it possible to display results in front 3 column and save result in csv format

for example

1-  4.2000 - 5.2000i
2  -3.2000 + 6.2000i
3  -5.2000 + 3.2000i
4  -3.2000 - 5.2000i
5  -6.2000 - 6.3000i
1  -2.3000 - 9.2000i
2   2.3000 - 6.2000i
3   2.3000 - 3.2000i
4   6.2000 - 6.3000i
5  3.2000 - 7.8000i

in my csv file now results will be saved in a+bi format ..instead of 4th and 5th columns only 4th columnm - results in a+bi format stored

[dpb]

Not so... readtable doc See Also says was introduced in R2013b.

readmatrix wasn't introduced until R2019a, but if you want to go old school for some mysterious reason, then

data=csvread(websave('plot.csv','https://www.mathworks.com/matlabcentral/answers/uploaded_files/1147855/plot.csv'),1,0);
X=data(:,1);
Y=[complex(data(:,4),data(:,5))];

Y = 
  -4.2000 - 5.2000i
  -3.2000 + 6.2000i
  -5.2000 + 3.2000i
  -3.2000 - 5.2000i
  -6.2000 - 6.3000i
  -2.3000 - 9.2000i
   2.3000 - 6.2000i
   2.3000 - 3.2000i
   6.2000 - 6.3000i
   3.2000 - 7.8000i

This way unless use a cell array can't combine X, Y because they're different classes (double, complex double); hence the table is really useful here.

[Image Analyst]

Can't you download the latest version?

If not, try this:

filename='plot.csv';
dataStructure = importdata(filename)
data = dataStructure.data;
x = data(:, 3)
% Get real component from column 4.
realValues = data(:,end-1);
% Get imaginary component from column 5.
imaginaryValues = data(:,end);
complexValues = realValues + 1i * imaginaryValues

[ramya]

Thank u sir this worked..but this complex values result has to be stored in same CSV file(last column) which i had uploaded in the beginning but with updated result

[dpb]

That again will be the reason to switch to using a table and writetable (below from the "See Also" version history at above link)

Version History

Introduced in R2013b

and, unless I'm sadly mistaken, R2013b will have predated R2018x.

None of the other output routines than the new(ish) writeXXX family knows how to write complex variables excepting by writing both the real and complex parts separately and physically inserting the connecting sign and "i". Nor can you store the various data types contained in the file of both double and the complex in a single variable to write in a single call excepting in a cell array other than in a table, so it's even more of an effort.

Fail to understand your reluctance to use the tools MATLAB does provide...

[Image Analyst]

Try this:

fullFileName = fullfile(pwd, 'plot.csv')
dataStructure = importdata(fullFileName)
data = dataStructure.data;
x = data(:, 3);
% Get real component from column 4.
realValues = data(:, 4);
% Get imaginary component from column 5.
imaginaryValues = data(:, 5);
complexValues = realValues + 1i * imaginaryValues

% Append the complex number after the last number
% Open the file for reading in text mode.
inputFileID = fopen(fullFileName, 'rt');
% Open an output file.
outputFileName = 'plot with complex numbers.txt';
outputFileID = fopen(outputFileName, 'wt');
% Read the first line of the file.
textLine = fgetl(inputFileID); % Read and discard first line
fprintf(outputFileID, '%s, Complex Number\n', textLine);
textLine = fgetl(inputFileID); % Get next line, which will have numbers on it.
lineCounter = 1;
while ischar(textLine)
    % Print out what line we're operating on in the command window.
    fprintf('%s, %f + i %f\n', textLine, realValues(lineCounter), imaginaryValues(lineCounter));
    % Now write to the file.
    fprintf(outputFileID, '%s, %f + i %f\n', textLine, realValues(lineCounter), imaginaryValues(lineCounter));
    % Read the next line.
    textLine = fgetl(inputFileID);
    lineCounter = lineCounter + 1;
end
% All done reading all lines, so close the file.
fclose(inputFileID);
fclose(outputFileID);
% Open the output text file.
winopen(outputFileName);