How to count how many x are greater than (x>0.2, 03 and 0.4) in a specific time?

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Hi Everybody,
I need to know how many (x>0.2,0.3&0.4)occurred at each hour. First, count it to make me able tabulate it (i.e. in time between 5-6, we observed 5 event(x>0.2) and so on) and then plot it as a bar. Please assume, x and y are defined as a column data in .xls format.
x y
0.05 10
0.1 10.1 (1 min)
0.02 10.2
0.2 10.3
0.012 10.4
. .
. .
. .
0.2 11
Thank you in advance,
  6 Comments
Ara
Ara on 18 Mar 2013
@ Walter: Exactly. As you said, It should be like 10.01 and 10.10. And the signal varied usually during an hour. It means between each minutes or even more minutes hard to find (x>0.2,0.3 or 0.4).
Image Analyst
Image Analyst on 18 Mar 2013
You'll have to read them in as text then and parse them into two separate numbers.

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Accepted Answer

Cedric
Cedric on 18 Mar 2013
Edited: Cedric on 18 Mar 2013
The following could be a solution..
>> x = rand(1,1e3)/2 ; % Fake x, for the example.
>> y = sort(rand(1,1e3)*23.99) ; % Fake y, for the example.
Build a cell array of distributions
>> bins = 0.05 : 0.1 : 0.45 ;
>> dists = arrayfun(@(h) hist(x(floor(y)==h), bins), 0:23, ...
'UniformOutput', false) ;
Test..
>> size(dists)
ans =
1 24
>> dists{1} % Distribution for the period [0-1h[.
ans =
6 6 9 12 6
>> dists{12} % Distribution for the period [11-12h[.
ans =
3 12 4 7 5
so for the period [11-12h[, 3 values are in the range [0,0.1[, 12 in the range [0.1, 0.2[, etc..
Note: you can achieve the same thing using a more basic approach, that you would have to put in a loop..
>> id_hr = y >= 11 & y < 12 ; % Index of y values (hrs) in the range 11-12h.
>> sum(x(id_hr) < 0.1) % Count # of corresponding x values below 0.1.
ans =
3
here we find the 3 that we found above as 1st element of dists{12}.
  6 Comments
Ara
Ara on 18 Mar 2013
Thank you VERY much. Let me play around with the plot and if you do not mind I will ask any question that I faced with.
Ara
Ara on 27 Sep 2020
Edited: Ara on 27 Sep 2020
Hi Cedric,
You wrote a FOR loop in my code. How to get rid of the loop and read data for one day of interest only without going to a circles again and again.
  • I would like to write my CV in Latex. Can you help me or do you have a template of it so that I can use it?
If I find the answer of this question, I will be the happiest woman in this World.
Please tell me how to correct it?
Best,
Ara

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More Answers (1)

Cedric
Cedric on 18 Mar 2013
You're welcome!
Well, at this point you should build a test dataset just to check, e.g.
>> s4 = [0.21, 0.21, 0.21, 0.32, 0.45, 0.45, 0.25] ;
>> time = [1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 2] ;
so there should be [3, 1, 2] associated with period [1-2h[, and [1, 0, 0] associated with period [2-3h[.
>> myHist = @(v) [sum(v>0.2 & v<=0.3), sum(v>0.3 & v<=0.4), sum(v>0.4)] ;
>> dists = arrayfun(@(h) myHist(s4(floor(time)==h)), 0:23, ...
'UniformOutput', false) ;
>> dists{1} % [0-1h[
ans =
0 0 0
>> dists{2} % [1-2h[
ans =
3 1 2
>> dists{3} % [2-3h[
ans =
1 0 0
It seems to be working. Then, using your dataset, you can check manually what happens with the period 5-6h. I show you here with the period 1-2h:
>> id_time = time >= 1 & time < 2 % Flag relevant times.
id_time =
1 1 1 1 1 1 0
this is a vector of logicals that we use then for indexing s4
>> s4_selection = s4(id_time)
s4_selection =
0.2100 0.2100 0.2100 0.3200 0.4500 0.4500
as you can see, these are the elements of s4 that correspond to a time in the range 1-2h[. Now we test myHist on this set of values
>> myHist(s4_selection)
ans =
3 1 2
It seems to be working.. let's check manually that the first count is correct
>> s4_selection > 0.2 & s4_selection <= 0.3
ans =
1 1 1 0 0 0
again, vector of logicals flagging relevant elements; counting them just means summing the vector of logicals (there is a conversion to numeric)
>> sum(s4_selection > 0.2 & s4_selection <= 0.3)
ans =
3
So it's working. Now ARRAYFUN repeats the same kind of operations with the small difference that instead of checking whether time is greater than h and smaller than h+1 for h=0:23, we test whether floor(time)==h.
Hope it helps; let me know if you are having troubles using this material!
  15 Comments
Ara
Ara on 22 Sep 2020
Edited: Ara on 27 Sep 2020
Hi Dr. Cedric Wannaz,
Thank you for providing useful explanation and the best solution back in 2013.
I still read through your code, programming and all you tought me about MATLAB and it is very useful so thanks again for being helpful all the time. However, I wish to contact you as I amfacing some questions about MATLAB programming and I need to send it to your email address. I wrote to your email address as you previuosly provided for me but I guess you no longer check your email!!!
I need to install Mozilla File the one that you have asked me to use in Australia. How can I install that file again?
I have some more questions and I wish to email it to you to discuss more details about MATLAB solution and I need to send the code to you but I could not find your emal address in your profile. Would you mind to provide your email address in your profile or here so that I can send my questions along with my code to you? You have my email address so you can write back to me in any of my email.
Thanks.
Ara

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