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

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Randy Chen
Randy Chen 2020-11-15
评论： Sai Veeramachaneni 2020-11-18
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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Sai Veeramachaneni
Sai Veeramachaneni 2020-11-17
Here are the few hints.
  1. Use readtable function to read csv file into matlab as a table.
  2. 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
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
Sai Veeramachaneni 2020-11-18
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);

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