How to use IF statements to find data greater than or equal to a certain amount

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AluminiumMan 2022-9-19

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https://ww2.mathworks.cn/matlabcentral/answers/1807840-how-to-use-if-statements-to-find-data-greater-than-or-equal-to-a-certain-amount

评论： AluminiumMan 2022-9-20

If you have a large amount of data, tens of millions of rows of data, how can you use IF statements in MATLAB to find specific data points that spike above a certain threshold?

Lets say for example you have a load of capacitance data against time. And you wan to find where the data spikes above 1 Farad. An example data table:

Time, Capacitance

1 uS, 0.3

2 uS, 0.5

3 uS, 0.8

4 uS, 1

5 uS, 1.3

6 uS, 1.4

7 uS, 1.2

8 uS, 0.9

9 uS, 0.5

You want to sift through this table and create a new variable that only includes data where the capacitance exceeds 1 Farad

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采纳的回答

Karim 2022-9-19

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1807840-how-to-use-if-statements-to-find-data-greater-than-or-equal-to-a-certain-amount#answer_1056325

编辑：Karim 2022-9-19

在 MATLAB Online 中打开

see below for a demonstration

Time = [1 2 3 4 5 6 7 8 9]';
Capacitance = [0.3 0.5 0.8 1 1.3 1.4 1.2 0.9 0.5]';
MyTable = table(Time,Capacitance)
MyTable = 9×2 table
    Time    Capacitance
    ____    ___________

     1          0.3    
     2          0.5    
     3          0.8    
     4            1    
     5          1.3    
     6          1.4    
     7          1.2    
     8          0.9    
     9          0.5    
% delete variables, just to show that we work with the data from the table
clearvars Time Capacitance
% set a treshold value
Treshold = 1;
% use some logice to find the values larger then the treshold (if you want
% to include it use >= instead of >
KeepMe = MyTable.Capacitance > Treshold;
% extract a part of the table using the logical array
NewTable = MyTable( KeepMe , : )
NewTable = 3×2 table
    Time    Capacitance
    ____    ___________

     5          1.3    
     6          1.4    
     7          1.2    

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Voss 2022-9-19

编辑：Voss 2022-9-19

在 MATLAB Online 中打开

CapacitanceData.mat

@AluminiumMan: You left off the second subscript, like the error message suggests:

A=B.C(C.Capacitance>Threshold,:);
%                            ^^ you need this part

Notice that @Karim's answer has it:

NewTable = MyTable( KeepMe , : )

Here's a demo with your mat file and variables, as given:

S = load('CapacitanceData.mat');
B = struct('C',S.CapacitanceData.RecordedCapacitanceData);
C = B.C;
Threshold = 1;
A=B.C(C.Capacitance>Threshold,:)
A = 3×2 table
    Time    Capacitance
    ____    ___________

     3          1.3    
     4          1.6    
     7          1.3    