How to replace columns in a datafile after performing mathematical operations to them?

I have a datafile having 40 columns and have to divide first column with a constant number (let say 5) and rest 39 columns with a different number (i.e. 7). So, I want to replace all the columns in a new datafile. Can you suggest any short method for it.

I am trying the following code but its not replacing the column, and just appending a column according to last given mathematical operation (i.e. here appending the new calculated 3rd column to the first column).

x=5; % a constant
y=7; %another constant
a = textread('file1.txt');
a1 = a(:,1)/x;
a2 = a(:,2)/y;
a3 = a(:,3)/y; %third column
save ('New_file1.txt','-ascii')
type('New_file1.txt')

Answer 1

[Voss]

x=5; % a constant
y=7; %another constant
a = readmatrix('file1.txt');

disp(a)

     1     2     3     4
     5     6     7     8
     9    10    11    12

new_a = a;
new_a(:,1) = new_a(:,1)/x;
new_a(:,2:end) = new_a(:,2:end)/y;

disp(new_a)

    0.2000    0.2857    0.4286    0.5714
    1.0000    0.8571    1.0000    1.1429
    1.8000    1.4286    1.5714    1.7143

writematrix(new_a,'New_file1.txt')

type('New_file1.txt')

0.2,0.285714285714286,0.428571428571429,0.571428571428571
1,0.857142857142857,1,1.14285714285714
1.8,1.42857142857143,1.57142857142857,1.71428571428571

[Shivu]

Thanks, but here writematrix is giving the data file separated by comma, whereas I want to store it in the previous column format.

How to do that?

[Walter Roberson]

there is a Delimiter option for writematrix()

[Voss]

@Shivu: As @Walter Roberson points out, try using ' ' (space) or '\t' (tab) or whatever the delimiter is in your original file (which I don't have):

new_a = rand(3);

writematrix(new_a,'New_file1.txt','Delimiter',' ')
type('New_file1.txt')

0.629923049782379 0.752624146887233 0.888350208105833
0.693355864220194 0.611977293643469 0.996243963795178
0.252144826948704 0.270950749648683 0.0546494299877862

writematrix(new_a,'New_file1.txt','Delimiter','\t')
type('New_file1.txt')

0.629923049782379	0.752624146887233	0.888350208105833
0.693355864220194	0.611977293643469	0.996243963795178
0.252144826948704	0.270950749648683	0.0546494299877862

[Shivu]

delimiter is not exactly placing it in columns. The output columns are quite messed up like this (even after using delimiter and tab)

0.4 0 6.508137e-06 0.08816902 0 -1.038636e-05 -1.35101e-05 6.832663e-09 5.346719e-05 1.111237e-06 -1.685898e-15 2.444716e-30 8.885579e-05 9.178685e-05 2.201578e-05 1.908472e-05

0.4666667 0 6.508137e-06 0.08816902 0 -1.011229e-05 -1.344511e-05 8.215198e-09 5.345097e-05 1.289439e-06 -2.139239e-15 -7.48446e-30 8.755713e-05 9.05559e-05 2.142161e-05

[Shivu]

Thanks to both of you, now I got it.

[Voss]

Glad you got it figured out!