Filter data conditionally based on previous row

Question

James Browne 2020-12-26

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/702587-filter-data-conditionally-based-on-previous-row

回答： Image Analyst 2020-12-26

Hi,

I have an array of test data. I want to filter out conditionally rows which contain a value in one column that does not increase over the previous row.

I was able to do this in excel using the following if statement:

=IF(AND(AN9<=0,(AN9<AN8)),AQ9,IF(AND(AN9>=0,(AN9>AN8)),AQ9,NA()))

I think I essentially need it to return a logical value of zero if the value in the row of the column doesn't increase over the previous. A simplified example of what I want to do is:

1.0 5.0

1.3 6.0

3.1 3.0

2.0 2.0

1.9 6.0

1.8 7.0

2.4 8.0

3.5 1.0

would return:

1.3 6.0

3.1 3.0

2.4 8.0

3.5 1.0

Is there a way that I can perform something similar in Matlab?

Thanks for any help you can provide!

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Answer 1

Image Analyst 2020-12-26

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/702587-filter-data-conditionally-based-on-previous-row#answer_584387

在 MATLAB Online 中打开

Try this. I think it's pretty self-explanatory.

m = [...
	1.0  5.0
	1.3  6.0
	3.1  3.0
	2.0  2.0
	1.9  6.0
	1.8  7.0
	2.4  8.0
	3.5  1.0 ]
col1Differences = [0; diff(m(:, 1))] % Get differences from one row to the next in column 1.
rowsToExtract = col1Differences > 0; % Get a logical vector of what rows have positive differences.
m2 = m(rowsToExtract, :) % Extract only those rows with a positive difference.