How to add a new column in a table and then write on a file only some columns?

Hi guys,

I've a simple code that reads data from a .csv file (atteched below). I have 56 rows, the first one is the header row and the the others contain data.

I want to create a new column contaning integer numbers that count the number of rows (so a column that contains: 1,2,3,4,..,55) and I want to call this column "index", then I want to put this one as first column of my table and I want to write it on a new .csv file by excluding the row called "name". Can you help me?

Here my code:

clear all; close all; clc;

% Definition of path names and file names  
file_data_ast = 'NEOs_asteroids.csv';

% Setting of data import options
opt = detectImportOptions(file_data_ast);
opt = setvaropts(opt,'Type','string');

% Import table of text data
Tab_ast_str = readtable(file_data_ast, opt);  
  
disp(['Asteroids (NEOs) no. : ',num2str(height(Tab_ast_str))]);

Asteroids (NEOs) no. : 28071

Here what I want to obtain:

Answer 1

[Turlough Hughes]

I like to use addvars and removevars for this:

T = readtable('https://uk.mathworks.com/matlabcentral/answers/uploaded_files/887485/NEOs_asteroids.csv');
T = removevars(T,'name');
T = addvars(T,(1:height(T)).','Before','pdes','NewVariableNames','index');
head(T)

ans = 8×11 table
    index    pdes      epoch         a          e         i         om        w         ma          q         ad  
    _____    ____    __________    ______    _______    ______    ______    ______    _______    _______    ______

      1       433    2.4596e+06    1.4583    0.22273    10.828     304.3     178.9      246.9     1.1335    1.7831
      2       719    2.4596e+06    2.6375    0.54696    11.575    183.86    156.23      278.2     1.1949    4.0801
      3       887    2.4596e+06    2.4732    0.57049    9.3941    110.43    350.49     86.607     1.0623    3.8841
      4      1036    2.4596e+06    2.6658    0.53312    26.678    215.52    132.43     140.65     1.2446    4.0871
      5      1221    2.4596e+06    1.9187    0.43584    11.883    171.32    26.644     261.04     1.0825     2.755
      6      1566    2.4596e+06    1.0781    0.82694    22.804    87.962    31.438    0.33029    0.18657    1.9696
      7      1580    2.4596e+06    2.1973    0.48716    52.079    62.292    159.51     16.629     1.1269    3.2677
      8      1620    2.4596e+06    1.2457    0.33536    13.338    337.18    276.95     300.49    0.82793    1.6634

To save it you can use:

writetable(T,'myNewTable.csv')

[Giuseppe]

Thanks!

Answer 2

[Enrico Gambini]

Hello Giuseppe.

To create your column of indexes you can do the following:

idx=[1:height(Tab_ast_str)];

then

Tab_ast_str.indexes=idx; %add the new column called "indexes" at the end of the table
Tab_ast_str=movevars(Tab_ast_str,'indexes','Before','pdes');%move your column at first position
Tab_ast_str=removevars(Tab_ast_str,'name'); %remove the column called "name"
writetable(Tab_ast_str,'new_table.csv'); %export the new table

Hope it helps!

[Giuseppe]

Thank you very much!