x=[1 2 3 4]y=[2 4 5 10]x1=[1,1.5,2.2,3.5,4] how to get previous matching value(from y) for x1 by refering x expected answer y1=[2 2 4 5 10] without forloop

for i=1:numel(x1)
    Idxfound = find (abs(x-x1(i)) < 0.00001); % abs(x-x1(i)) < 0.1
    if isempty(Idxfound)
        Idxfound=find(x < x1(i));
        if isempty(Idxfound)
            if i==1
                y1(i) = y(1);
            else
                y1(i)=y1(i-1);
            end
        else
            Idxfound=Idxfound(end);
            y1(i) = y(Idxfound);
        end
    else
        y1(i) = y(Idxfound);
    end
end
end

Answer 1

[Stephen23]

x = [1,2,3,4]; 
y = [2,4,5,10];
x1 = [1,1.5,2.2,3.5,4];
%y1=[2,2,4,5,10];
y1 = interp1(x,y,x1,'previous')

y1 = 1×5

2 2 4 5 10

[deepika Sridhar]

If NaN comes in the result array.

how to replace this Nan with empty value.

[Torsten]

y1(isnan(y1)) = [ ]

[deepika Sridhar]

Result of this interpolation is double array.

[Torsten]

y=[0 5 7 NaN 4 9 NaN];
y(isnan(y))=[ ];
y

y =

0 5 7 4 9

Answer 2

[KSSV]

x=[1 2 3 4]; 
y=[2 4 5 10];
x1=[1,1.5,2.2,3.5,4] ;
% y1=[2 2 4 5 5] ;
y1 = interp1(x,y,x1)

y1 = 1×5

2.0000 3.0000 4.2000 7.5000 10.0000

[deepika Sridhar]

Hi,

I dont want new interpolated values,

I want exact matched value or previous value

[KSSV]

x=[1 2 3 4]; 
y=[2 4 5 10];
x1=[1,1.5,2.2,3.5,4] ;
% y1=[2 2 4 5 5] ;
y1 = y(round(x1))  

y1 = 1×5

2 4 4 10 10

idx = knnsearch(x',x1') ;
y1 = y(idx)

y1 = 1×5

2 2 4 5 10

[deepika Sridhar]

to use knnsearch we need

following tool box right?

Statistics and Machine Learning Toolbox

Text Analytics Toolbox

Is there any way without that

[KSSV]

x=[1 2 3 4]; 
y=[2 4 5 10];
x1=[1,1.5,2.2,3.5,4] ;
% y1=[2 2 4 5 5] ;

n = length(x1); 
idx = zeros(n,1) ;
for i = 1:n
    [val,id] = sort(abs(x-x1(i))) ;
    idx(i) = id(1) ;
end
y1 = y(idx) 

[deepika Sridhar]

Hi,

I have lakhs of data in x1

is there any option without forloop

Thanks in advance