How to use find() in MATLAB in order to find decimals

问题

I am given a table with two columns - one is P_in and the other P_out:

P_in  = table(:,1);
P_out = table(:,2);

I am also given a subset of P_in, which I call P_in2. I want to find the corresponding value of P_out that belongs to P_in2.

I tried find():

P_out2_idx = find(table(P_in2,2));
P_out2     = table(P_out2,idx,2);

But find() can only deal with integers. My table however, does not show integers, but decimals. Here are three lines from the table:

-13.02    49.6
-12.52    49.9
-12.02    50.18

So even rounding the P_in2 values wouldn't work.

回答1:

Using ismember is good for finding multiple indices if your numbers are integers. For floating-point numbers a safer way is using ismembertol:

isInP_in2 = ismembertol(P_in, P_in2, eps);
P_out2 = P_out(isInP_in2);

The returned array isInP_in2 is a logical array the size of P_in, which is true at the indices where values in P_in2 are found, and false otherwise.

The third argument is the tolerance used for comparisons (here we take the floating-point relative accuracy eps). For example, searching for a single index using find would be done:

idx = find(abs(P_in - P_in2(1)) < eps);

来源：https://stackoverflow.com/questions/41609994/how-to-use-find-in-matlab-in-order-to-find-decimals