Question on using interpolate function

I've the following

x = [1 2 3 4 5 6];
data = [0.1 0.2 0.3 0.4 0.4 0.4]; 
vq1 = interp1(data,x,0.4)

I want to find the x value at which data has 0.4 (first occurence).

I used interpolate. But the following error occurS

The grid vectors must contain unique points.

Any suggestions on how to proceed when data doesn't contain uniqe values will be helpful

[Deepa Maheshvare]

I'm still expecting answers for this post. Unfortunately, the following suggestions didn't help.

Answer 1

[KSSV]

Use logical indexing:

x = [1 2 3 4 5 6];
data = [0.1 0.2 0.3 0.4 0.4 0.4]; 
vq1 = x(abs(data-0.4)<10^-5)

[Deepa Maheshvare]

I'm looking for an interpolation function. It may happen that Ive to check for a value of 0.45 that is not present in data

Answer 2

[Bhaskar R]

"I want to find the x value at which data has 0.4 (first occurence)."

match_loc = find(data == 0.4);
val = x(x == match_loc(1));     % first occurance of 0.4

[Deepa Maheshvare]

What if I have to check for 0.45?