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Obtaining the percentile 95 of a matrix and then plotting it

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1

EDIT:
I have been asked to add more detail. Originally I have a 360x180 matrix, and in it there are data of E-P values, these values stand for Evaporation (E) and Precipitation (P), and they basically indicate sources (E-P>0) and sinks(E-P<0) of moisture. In order to obtain the most important sources of moisture I have to take only the positive values, and I want to obtain the percentile 95 of these values, then plot the values which are above this threshold, since I wanted to do a reproducible example I used the peaks data:

I have done this in MATLAB but if it can be made on R it works for me as well.

I have an example 49x49 matrix like this:

a = peaks; 
pcolor(a);
caxis([-10 10]); 
cbh=colorbar('v');
set(cbh,'YTick',(-10:1:10))

And it shows something like this

What I want to do is to obtain the percentile 95 of only the positive values, and then plotting them.

How can I do this? and also, what would it be better: To replace all the values less than zero with 0's or Nan's??

r matlab statistics quantile

share|improve this question

edited Mar 9 at 23:30

Ann M

asked Mar 8 at 22:39

Ann MAnn M

9610

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I have added more detail, hopping that it makes it more clear.
  
  – Ann M
  Mar 9 at 23:31
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I think the question is clear now, voting to reopen.
  
  – Cris Luengo
  Mar 10 at 0:15
  

  
  
  
  

add a comment | 

1

EDIT:
I have been asked to add more detail. Originally I have a 360x180 matrix, and in it there are data of E-P values, these values stand for Evaporation (E) and Precipitation (P), and they basically indicate sources (E-P>0) and sinks(E-P<0) of moisture. In order to obtain the most important sources of moisture I have to take only the positive values, and I want to obtain the percentile 95 of these values, then plot the values which are above this threshold, since I wanted to do a reproducible example I used the peaks data:

I have done this in MATLAB but if it can be made on R it works for me as well.

I have an example 49x49 matrix like this:

a = peaks; 
pcolor(a);
caxis([-10 10]); 
cbh=colorbar('v');
set(cbh,'YTick',(-10:1:10))

And it shows something like this

What I want to do is to obtain the percentile 95 of only the positive values, and then plotting them.

How can I do this? and also, what would it be better: To replace all the values less than zero with 0's or Nan's??

r matlab statistics quantile

share|improve this question

edited Mar 9 at 23:30

Ann M

asked Mar 8 at 22:39

Ann MAnn M

9610

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I have added more detail, hopping that it makes it more clear.
  
  – Ann M
  Mar 9 at 23:31
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I think the question is clear now, voting to reopen.
  
  – Cris Luengo
  Mar 10 at 0:15
  

  
  
  
  

add a comment | 

EDIT:
I have been asked to add more detail. Originally I have a 360x180 matrix, and in it there are data of E-P values, these values stand for Evaporation (E) and Precipitation (P), and they basically indicate sources (E-P>0) and sinks(E-P<0) of moisture. In order to obtain the most important sources of moisture I have to take only the positive values, and I want to obtain the percentile 95 of these values, then plot the values which are above this threshold, since I wanted to do a reproducible example I used the peaks data:

I have done this in MATLAB but if it can be made on R it works for me as well.

I have an example 49x49 matrix like this:

a = peaks; 
pcolor(a);
caxis([-10 10]); 
cbh=colorbar('v');
set(cbh,'YTick',(-10:1:10))

And it shows something like this

What I want to do is to obtain the percentile 95 of only the positive values, and then plotting them.

How can I do this? and also, what would it be better: To replace all the values less than zero with 0's or Nan's??

r matlab statistics quantile

share|improve this question

edited Mar 9 at 23:30

Ann M

asked Mar 8 at 22:39

Ann MAnn M

9610

a = peaks; 
pcolor(a);
caxis([-10 10]); 
cbh=colorbar('v');
set(cbh,'YTick',(-10:1:10))

share|improve this question

edited Mar 9 at 23:30

Ann M

asked Mar 8 at 22:39

Ann MAnn M

9610

share|improve this question

edited Mar 9 at 23:30

Ann M

asked Mar 8 at 22:39

Ann MAnn M

9610

asked Mar 8 at 22:39

Ann MAnn M

9610

asked Mar 8 at 22:39

Ann MAnn M

9610

1 Answer
1

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oldest

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0

If you have the statistics toolbox, you can use the function prctile to obtain a percentile. I don't have this toolbox, so I wrote my own version (a long time ago) based on the code for the function median. With either prctile or percentile you can do:

a = peaks;
t = percentile(a(a>0),95);
b = a > t;

subplot(1,2,1)
pcolor(a);
subplot(1,2,2)
pcolor(b);

a(a>0) is a vector with all the positive values in a. t is the 95th percentile of this vector.

share|improve this answer

answered Mar 11 at 6:25

Cris LuengoCris Luengo

22.5k52253

add a comment | 

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0

If you have the statistics toolbox, you can use the function prctile to obtain a percentile. I don't have this toolbox, so I wrote my own version (a long time ago) based on the code for the function median. With either prctile or percentile you can do:

a = peaks;
t = percentile(a(a>0),95);
b = a > t;

subplot(1,2,1)
pcolor(a);
subplot(1,2,2)
pcolor(b);

a(a>0) is a vector with all the positive values in a. t is the 95th percentile of this vector.

share|improve this answer

answered Mar 11 at 6:25

Cris LuengoCris Luengo

22.5k52253

add a comment | 

0

If you have the statistics toolbox, you can use the function prctile to obtain a percentile. I don't have this toolbox, so I wrote my own version (a long time ago) based on the code for the function median. With either prctile or percentile you can do:

a = peaks;
t = percentile(a(a>0),95);
b = a > t;

subplot(1,2,1)
pcolor(a);
subplot(1,2,2)
pcolor(b);

a(a>0) is a vector with all the positive values in a. t is the 95th percentile of this vector.

share|improve this answer

answered Mar 11 at 6:25

Cris LuengoCris Luengo

22.5k52253

add a comment | 

If you have the statistics toolbox, you can use the function prctile to obtain a percentile. I don't have this toolbox, so I wrote my own version (a long time ago) based on the code for the function median. With either prctile or percentile you can do:

a = peaks;
t = percentile(a(a>0),95);
b = a > t;

subplot(1,2,1)
pcolor(a);
subplot(1,2,2)
pcolor(b);

a(a>0) is a vector with all the positive values in a. t is the 95th percentile of this vector.

share|improve this answer

answered Mar 11 at 6:25

Cris LuengoCris Luengo

22.5k52253

a = peaks;
t = percentile(a(a>0),95);
b = a > t;

subplot(1,2,1)
pcolor(a);
subplot(1,2,2)
pcolor(b);

share|improve this answer

answered Mar 11 at 6:25

Cris LuengoCris Luengo

22.5k52253

answered Mar 11 at 6:25

Cris LuengoCris Luengo

22.5k52253

answered Mar 11 at 6:25

Cris LuengoCris Luengo

22.5k52253