Create a function from a table

Suppose I have a matrix

A = [ 3 0.1; 1 0.2; 2 0.3];

I now want to have a function that takes an entry of the first column and gives the entry in the second column.

In other words, I want to have a matrix B where, for each element in the first column, its second column is the entry of the corresponding second column in A. For example,

B = [ 2 0.3; 2 0.3; 3 0.1; 1 0.2];

Please advise.

Answer 1

[Star Strider]

Try this:

A = [ 1 0.1; 2 0.2; 3 0.3];
A2fcn1 = @(k) A(k,2);

SecondColumn = A2fcn1(2)

SecondColumn =
    0.2000

If you want to interpolate instead, use the interp1 (link) function.

[alpedhuez]

Thank you. Let me work on it.

[Star Strider]

As always, my pleasure.

Answer 2

[Walter Roberson]

Given any finite sets of example values, there are aleph-one (the infinity of cardinal numbers) functions that will exactly calculate the given values to within round-off error. There is no way to automatically choose between these functions as one being "better" than the other -- not unless you specify before-hand which forms of function are to be preferred.

[alpedhuez]

Not that complicated. The question is how to efficiently fill in the second column of B given A and the first column of B.