Can I add new column (calculated from first column) to a text file ?

Dear all, Please I have a text file has one column and many rows. I need to add new column which is calculated from the first column (the difference between the new set of rows and old set of rows which means the change in the first column. for example, the set of rows below consists from three rows each ( the first zeros should be for both columns).I need to apply this for the text file attached.

0 0

0 0

0 0

1 (1-0)

3 (3-0)

6 (6-0)

2 (2-1)

5 (5-3)

8 (8-6)

Many thanks

Answer 1

[Star Strider]

This seems to do what you want:

B = load('ND B.txt', '-ascii');
New_Col = [B(4:end) - B(1:end-3); zeros(3,1)];
New_B = [B New_Col];

The last 3 rows of ‘New_Column’ I set to zero to make it possible to concatenate it with the existing ‘B’. You may want to append them to the beginning instead, or set them to NaN. The point is the columns have to have equal length to concatenate them.

[ND]

Thank you Star,

Please how can I set them with zeros at the beginning instead ? Also, I do not know how many rows exactly ,but I can specify the number of rows at each set.

[Star Strider]

My pleasure.

To put the zeros at the beginning of the new column, this works:

New_Col = [zeros(3,1); B(4:end) - B(1:end-3)];

No other changes to my code are necessary.

To change the number of rows to offset, I introduced the ‘NrRows’ variable. This works, and also puts the zeros at the beginning of ‘New_Col’:

B = load('ND B.txt', '-ascii');
NrRows = 4;
New_Col = [zeros(NrRows-1,1); B(NrRows:end) - B(1:end-NrRows+1)];
New_B = [B New_Col];

I tested this. It should do what you want.

[ND]

many thanks, Sorry can you a bit clarify this line :

New_Col = [zeros(3,1); B(4:end) - B(1:end-3)];

As I can not specify the number of rows , but I know how many rows at each set.

Best regards

[Star Strider]

The ‘New_Col’ variable subtracts the values of ‘B’ from the 4th (or in the new code ‘NrRows’) row from the beginning of ‘B’ to the end of ‘B’, from the values of ‘B’ from the 1st row of ‘B’ to the 4th (or in the new code ‘NrRows’) row from the end of ‘B’, producing a column vector of the differences. It also adds the required column vector of zeros at the beginning to make the number of rows in ‘New_Col’ equal to the original row length of ‘B’. The code does not need to know how long ‘B’ is. It only needs to know how many rows you want to offset to do the subtraction. That is set by the ‘NrRows’ variable, that you can set to almost any value you want. (It must be greater than zero and less than the length of ‘B’.)

[ND]

thank you very much

[Star Strider]

My pleasure!

[ND]

Please now I want to do summation of column one and two (which is created) and write the column one and the sum in a new text file , so the result would be a text file with only two columns.

Thanks

[Star Strider]

This is actually a new Question and should be posted as such.

Also, please give an example of what you want to do. Your description is not clear.