Creation of new column

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Pap 2011-3-20

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 I have an input file (ex.txt) which contains three columns
0 0
2 5
3 6
4 4
1 3
4 8
2 9
5 5

I need to save the sum of the previous row columns into a fourth column in the input txt file, in order to look like

Any Hint?

Panos

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Paulo Silva 2011-3-20

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在 MATLAB Online 中打开

   %code
   a=[0 0 0
2 5
3 6
4 4
1 3
4 8
2 9
5 5]
  b=[0;sum(a,2)];
  c=[a b(1:end-1)];
%result
c =
   0     0     0
   2     5     0
   3     6     8
   4     4    11
   1     3    11
   4     8     8
   2     9    18
   5     5    16

How can I put in the above code the argument that if the value of current row (third column) is equal to the value of previous row and previous value of column 4 is 'BUY' then put BUY and if it is SELL ( otherwise) put 'SELL'.

Also where do you define 1,0 ( in order to change it to BUY SELL).

And may I also ask which code defines the first value only of cilumn 4, in order to apply then the above code.

Thanks a lot for the great help.

Pap 2011-3-21

Note that your data set is different from the above ( actually is my first one. The latest one has a case where two elements of column thre are equal and thus someone has to examine the previous value of column four)

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Walter Roberson 2011-3-20

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Hints: fopen, textscan, fprintf,

You will not be able to do this in a single output (not in any clean manner), as you cannot construct a numeric array that has a different number of columns.

You appear to be missing a final output line that has just a 12 by itself, representing the sum of the three values on the last line of the input file.