calculate mean using while and iteration?

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Madan Kumar
Madan Kumar 2019-4-30
评论： Madan Kumar 2019-5-3
Hi,
I have data of ~3500x2. I want to calulate mean of second column for a particular condition in first column using 'while'.
let data (a, b) be like
0.5 1.8
0.6 1.5
0.9 1.8
1.0 1.5
1.1 1.4
1.2 1.4
1.5 1.6
1.8 1.2
2.1 1.2
2.3 1.3
2.4 1.5
2.6 1.8
2.9 2.0
3.0 3.0
3.12 3.2
3.15 1.9
3.16 1.7
3.18 2.2
I need to calculate mean of b, if a> 0.5 and a<1.5. Then increase 'a' by 1 and calculate mean of b (i.e for a > 1.5 and a<2.5) and so on. It may be a silly question but I am stuck with it. My code is
del=0.5;
k=1;
a(k)=1;
while(a(k) >(a(k)-del) && a(k)< (a(k)+del))
xn(k)=mean(b(k));
k= k+1;
a(k)=a(k)+1;
end
but it shows error Index exceeds array bounds.
Error in untitled (line 12)
a(k)=a(k)+1;
Thank you for your help.
  2 个评论
David Wilson
David Wilson 2019-4-30
编辑：David Wilson 2019-4-30
My code below is a bit ugly, but I think it does what you want:
cutoff = [0.5 1.5]; % band of interest
maxA = ceil(max(a))+0.5;
bmean = [];
for i=1:maxA
idx = find(a>cutoff(1) & a<cutoff(2));
bmean(i) = mean(b(idx));
cutoff = cutoff+1;
end
The means of column "b" are in variable bmean.
I note that you specified strict < as opposed to <= which may, or may not be what you really want.
Note that column a need not be sorted in increasing order.

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采纳的回答

Rik
Rik 2019-4-30
So you want to calculate these values?
xn(1)=mean(b(a>0.5 & a<1.5));
xn(2)=mean(b(a>1.5 & a<2.5));
xn(3)=mean(b(a>2.5 & a<3.5));
etc?
You don't need a while loop for that:
a=[0.5 0.6 0.9 1.0 1.1 1.2 1.5 1.8 2.1 2.3 2.4 2.6 2.9 3.0 3.12 3.15 3.16 3.18];
b=[1.8 1.5 1.8 1.5 1.4 1.4 1.6 1.2 1.2 1.3 1.5 1.8 2.0 3.0 3.2 1.9 1.7 2.2];
del=0.5;
xn=zeros(1,ceil(max(a-del)));
for k=1:size(xn,2)
xn(k)=mean(b(a>(k-del) & a<(k+del)));
end
  4 个评论
显示 2更早的评论
Stephen23
Stephen23 2019-4-30
编辑：Stephen23 2019-4-30
"Suppose, I need xn(0.5)=... "
You can't. Indices must be whole integers greater than zero.
Either change del to 0.25 and leave it at that, or write a function which lets you have any input values that you desire. But you certainly cannot have indexing with non-integer values.

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更多回答（1 个）

KSSV
KSSV 2019-4-30
Why loop? YOu can use inbuilt in mean. Let a,b be your columns.
idx = a>0.5 & a<1.5 ;
mean(b(idx))

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