how to select a row of data from a csv file that is imported into Matlab?

Question

Randy Chen 2020-11-15

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https://ww2.mathworks.cn/matlabcentral/answers/648163-how-to-select-a-row-of-data-from-a-csv-file-that-is-imported-into-matlab

评论： Sai Veeramachaneni 2020-11-18

采纳的回答： Sai Veeramachaneni

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I need to read in a csv file and utilize a function that is built into matlab:

[a,ecc,incl,RAAN,argp,nu,truelon,arglat,lonper] = ijk2keplerian(r_ijk, v_ijk)

Here is what my csv file looks like:

how should I import this csv file into matlab and then make a set of row vectors r = [rx,ry,rz] and v = [vx,vy,vz] such that I can use the above function directly?

I also want to create a plot of all six elements returned by the ijk2keplerian(r_ijk, v_ijk) function vs time. How should I make a for loop such that the function ijk2keplerian(r_ijk, v_ijk) returns all 6 elements into lists so I can plot each of the six elements vs time (on the same plot with legend)??

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Answer 1

Sai Veeramachaneni 2020-11-17

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https://ww2.mathworks.cn/matlabcentral/answers/648163-how-to-select-a-row-of-data-from-a-csv-file-that-is-imported-into-matlab#answer_546818

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Here are the few hints.

Use readtable function to read csv file into matlab as a table.
Get the required column of the table using tablevariablename.columnname

Example

filename='file.csv';
table_data=readtable(filename);
r=[table_data.rx(1),table_data.ry(1),table_data.rz(1)];
v=[table_data.vx(1),table_data.vy(1),table_data.vz(1)];
[a,ecc,incl,RAAN,argp,nu,truelon,arglat,lonper] = ijk2keplerian(r, v)

References: https://www.mathworks.com/help/matlab/ref/readtable.html

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Randy Chen 2020-11-17

i see, i have one last quesiton. So i want to create a plot of each of the elements[a,ecc,incl,RAAN,argp,nu,truelon,arglat,lonper] vs time given in the CSV. I just tried the for loop but it's not returning the values of [a,ecc,incl,RAAN,argp,nu,truelon,arglat,lonper] into a column vector for each element. How should I modify the codes so that I can get a plot of each of the 6 elements vs time? (6 lines on 1 graph with legend perhaps)

Sai Veeramachaneni 2020-11-18

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You can build row vector inside for loop and later use this vector to plot the graphs.

See below code for your reference.

column_a=[]
column_ecc=[]
column_incl=[]
for i = 1:length(table_data.rx)
    r=[table_data.rx(i),table_data.ry(i),table_data.rz(i)];
    v=[table_data.vx(i),table_data.vy(i),table_data.vz(i)];
    [a,ecc,incl,RAAN,argp,nu,truelon,arglat,lonper] = ijk2keplerian(r, v);
    column_a=[column_a a]; %Storing value a inside row vector
    column_ecc=[column_ecc ecc];
    column_incl=[column_incl incl];
    %Add remaining lines 
end
plot(column_a,t)%t is the time 
plot(column_ecc,t);
plot(column_incl,t);