Calculating Max and Min of subsets of data

Hi,

I have 8 columns of 63000 data points that I want to calculate the max and min every 57, 56, 56 ,56, 57, 56,... subset.

I know there should be an easier way then doing several repeating loop layers to take these subsets of varying length and calculating the max and min.

Any help would be most appreciative.

 Cheers,
  Elliott

Edit: not that it matters much but it's actually 63553 x 7, I was counting my timestamp data in the 8th column, but I don't need the averages of that.

[Andrei Bobrov]

A = randi(78,63553,7);
a = [57, 56, 56 ,56].';

s = size(A);
sa = sum(a);
t = cumsum(a) < rem(s(1),sa);
i1 = [repmat(a,fix(s(1)/sa),1);a(t);rem(s(1),sa) - a(t)];

i4 = cumsum(i1); 
i3 = i4 - i1 + 1;
Aminmax = zeros(numel(i3),s(2),2);
for jj = 1:numel(i3)
    d = A(i3(jj):i4(jj),:);
    Aminmax(jj,:,:) = cat(3,min(d),max(d));
end

Answer 1

[Azzi Abdelmalek]

x=rand(63000,8);
id1= 3*56+57 ;
s=reshape(x',8,id1,[]);minx=[];
for k=1:size(s,3)
  minx=[minx min(min(s(:,1:57,k))) min(min(s(:,58:113,k)))...
        min(min(s(:,114:169,k))) min(min(s(:,170:225,k)))];
  maxx=[maxx max(max(s(:,1:57,k))) max(max(s(:,58:113,k)))...
        max(max(s(:,114:169,k))) max(max(s(:,170:225,k)))]
end

[Elliott Brecht]

I tried using reshape earlier, but came upon the problem of it not dividing my matrix evenly so I receive back errors

Error using reshape Product of known dimensions, 1800, not divisible into total number of elements, 508424

Is there away around this?

[Azzi Abdelmalek]

Is there a problem with the code?

[Elliott Brecht]

No the code works, but my matrix doesn't fit the reshape. So I'm wondering if I should edit out some of the final elements or if there is a way to have it reshape even though the matrix is an odd number

[Azzi Abdelmalek]

there is a way to do it by adding nan or zeros to your array

[Elliott Brecht]

Thanks, that's what I assumed, but wanted confirmation.

[Elliott Brecht]

Hmmm.. I'm getting more undefined errors and the subsets seem small and have elements that I'm not sure where it's getting them, I know what the Max and Min should be for several of the subsets and I'm getting different results.

[Azzi Abdelmalek]

I think it's better if we cut then adding nan, because nan or zeros will change min max values

clear
n=63553
y=rand(n,8);
id1= 3*56+57;
c=floor(n/id1)
if c~=n/id1
  x=y(1:c*id1,:);
  xr=y(c*id1+1:end,:);
else
  x=y
  xr=[];
end

% x is 63450x8 and xr is 103x8

Answer 2

[Laura Proctor]

Is your matrix 7875 x 8?

Also, when you say "every 57" does that mean the first 57 rows? The first 57 elements in the column? The first 57 elements going row wise?

If you, for example, wanted to calculate the max/min for the first 57 rows, the syntax is simply:

xMax1 = max(x(1:57,:));
xMin1 = min(x(1:57,:));

[Elliott Brecht]

My Matrix is 63553 x 8 I want to separately get the max, min of the first 57 elements of each column, then the next 56 elements, next 56 elements, etc. repeated until end of data set.

[Elliott Brecht]

This works great, but it seems I would need to loop and still calculate each subset. Is there a way to automate the numbers, xMax1 = max(x(1:57,:)) max(x(58:113,:)), continued, continued without defining the matrix locations as variables and increasing them in a loop?

Answer 3

[Azzi Abdelmalek]

%corrected code

cclear
n=63553
y=rand(n,8);
id1= 3*56+57;
c=floor(n/id1)
if c~=n/id1
x=y(1:c*id1,:);
xr=y(c*id1+1:end,:);
else
x=y
xr=[];
end
s=reshape(x',8,id1,[]);minx=[];maxx=[]
for k=1:size(s,3)

    i1=1:57,i2=58:113,i3=114:169,i4=170:225;
    minx=[minx min(min(s(:,i1,k))) min(min(s(:,i2,k)))...
        min(min(s(:,i3,k))) min(min(s(:,i4,k)))];
    maxx=[maxx max(max(s(:,i1,k))) max(max(s(:,i2,k)))...
        max(max(s(:,i3,k))) max(max(s(:,i4,k)))];
end
idxr=size(xr,1);test=57;
idxr1=idxr
x0=1
while idxr1-test>0
  xr1=xr(x0:x0+test-1,:)
  minx=[minx min(min(xr1))];
  maxx=[minx max(max(xr1))];
  idxr1=idxr1-test
  x0=x0+test;
  test=56;
end
if idxr1>0
  xr1=xr(x0:end,:)
  minx2=[minx min(min(xr1))];
  maxx2=[minx max(max(xr1))];
end

% or using only "while"

 clear
n=63553;
xr=rand(n,8);
load ansm 
xr=y;
numx=round(n/(3*56+57))+1;
idxr1=size(xr,1);
v=repmat([57 56 56 56],1,numx);
k=1;minx=[];maxx=[];test=57;x0=1;
while idxr1-test>0 
  xr1=xr(x0:x0+test-1,:);
  minx=[minx min(min(xr1))];
  maxx=[minx max(max(xr1))];
  idxr1=idxr1-test
  k=k+1;x0=test+x0;
  test=v(k);  
end
if idxr1>0
xr1=xr(x0:end,:);
minx1=[minx min(min(xr1))];
maxx1=[minx max(max(xr1))];
end

[Elliott Brecht]

Thanks! Made some minor edits but it worked great. Thanks a ton!

[Azzi Abdelmalek]

error fixed