How to choose data with conditions?

Hello!! I'm new in programming world and I’m trying to select the data of a column with some condition; I need to select only when the data is increasing in the column, and when is decreasing in the same column. I did it in excel with: =IF((BA3-BA2)<0,BA2+(BA3-BA2)) --- for decreasing, and =IF((BA3-BA2)>0,BA2+(BA3-BA2)) for increasing. But I’m not able to do it in mat lab with the entire column.

If somebody can help me I really appreciative!

data = xlsread('Data1.xlsx')

data = 213×1

109.4632 109.3436 108.9267 108.2206 107.2488 106.1058 104.9447 103.8366 102.7987 101.7733

Answer 1

[Sulaymon Eshkabilov]

This can be done a few different ways. MATLAB has several very efficient built-in functions to compute any value change dynamics. In your exercise, you would need to take the following steps:

Step 1. Data import

D = readmatrix('Data1.xlsx')'

Step 2. Compute the data chaneg dynamics

dD = diff(D);

Step 3. Find out if the data is increasing or decreasing order

IDX1 = find(dD>0);  % Locate Indices for increase
IDX2 = find(dD<0);  % Locate Indices for decrease

Step 4. Do something ...

[Mario]

Thanks so much, it works. It is possible to keep help me it would be great. Now that I located the increasing and decreasing data, I need to sum all the increasing data and all the decreasing data. I'm not able to do it when I sum the location (IDX1 or IDX2).

Also, I was trying to identify in the plot (with some symbols) the increasing and decreasing data, without successful results. How can I do it??

Thanks again, have a nice day

Mario N.L.

Answer 2

[Cris LaPierre]

Create a logical array and use that to select the values you want. See Ch 11 of MATLAB Onramp.

A simple example

A = [109.4632
  109.3436
  108.9267
  108.2206
  107.2488];
% logical array of locations where sequential rows are increasing or
% decreasing (will be one row shorter than A)
d = diff(A);
ind =  d~=0;

% Create a new vector based on your formula: next value is current value
% plus difference of next row and current row
B = A([ind;false]) + d(ind)

B = 4×1

109.3436 108.9267 108.2206 107.2488