How to perform individual operation on a Column of data from excel file?

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Khondokar Fida Hasan
评论： Walter Roberson 2017-10-23
I am intended to perform a separate operation (adding/subtracting some values) on Positive and Negative value from an Excel dataset using Matlab. To read the column I use the following code
num = xlsread('testdata.xls', 'B:B');
it reads fine and when I ask 'num' it shows the data. However, the data are having positive and negative values. I want to add some values to negative dataset and substruct from the positive dataset by keeping their position alike so that I can reconstruct a graph having exactly the same pattern. I have made two attempts:
1. Using logical indexing I can separate the positive and negative values and then perform the operation but can't combine them in the same order, something like following
idx = num<0;
neg = num(idx)+ 1.0e-08
pos = num(~idx)- 1.0e-08
2. If-else also not working at all:
if (num<0)
num = num +1
elseif(num>0)
num = num +2
end
Any help, please?

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采纳的回答

KSSV
KSSV 2017-10-23
编辑：KSSV 2017-10-23
idx = num<0;
num(idx) = num(idx)+ 1.0e-08
num(~idx)= num(~idx)- 1.0e-08

更多回答（1 个）

Walter Roberson
Walter Roberson 2017-10-23
idxneg = num<0;
num(idxneg) = num(idxneg)+ 1.0e-08;
idxpos = num>0;
num(idxpos) = num(idxpos)- 1.0e-08;
I did not use ~idxneg because ~idxneg would include num == 0 exactly, but exact zeros are not positive values.
There is a shortcut for this code:
num = num - sign(num) * 1.0e-08;
This even leaves 0 unchanged.
  2 个评论
Khondokar Fida Hasan
Khondokar Fida Hasan 2017-10-23
This shortcut seems wonderful but in my case the operation (adding value) is different. Though in aforementioned case I use 1.0e-08 for every case, but I want to perform different adjustment for a different case.
Walter Roberson
Walter Roberson 2017-10-23
offsets = [1.0e-08, 0, -8.7e-9];
num = num + offsets(2 + sign(num));
provided that the breakpoints are still negative, 0, positive

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