Interpolate specific columns of data

Question

I have a txt file with 3 columns of data:

x y1 y2

How do I import the file then create 2 functions, one interpolated with {x,y1} values and the other interpolated with {x,y2} values?

This is the sort of thing I want to achieve (in pseudocode):

Import "data.txt" into A
f1 = Interpolation(A,{x,y1})
f2 = Interpolation(A,{x,y2})

Did you happen to look up the Import documentation? This and its subpage on basic formats (search for "Table") would be a good starter.Interpolation also has a very readable doc page. To get the table you obtain after importing into separate columns, you need Transpose. Please, try to reach a minimum proficiency level of the language by reading the documentation before asking questions. — Sjoerd C. de Vries, Jun 22, 2012 at 12:39
For taking parts of arrays you could check out the documentation of Part — Heike, Jun 22, 2012 at 12:45

Mr.Wizard · Accepted Answer · 2012-06-22 19:33:56Z

6

Maybe something like

a = Transpose[Import["data.txt", "Table"]];

f1 = Interpolation[{a[[1]], a[[2]]} // Transpose];
f2 = Interpolation[{a[[1]], a[[3]]} // Transpose];

might work?

Alternatively,

a = Import["data.txt", "Table"];

f1 = Interpolation[Drop[#, {3}] & /@ a];
f2 = Interpolation[Drop[#, {2}] & /@ a];

or even

f1 = Interpolation[ a[[All, {1, 2}]] ];
f2 = Interpolation[ a[[All, {1, 3}]] ];

Mr.Wizard

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answered Jun 22, 2012 at 12:38

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$\begingroup$ For the second one, you can also use a[[All,{1,2}]] and a[[All, {1,3}]] instead of Drop[...]&/@a. $\endgroup$
– Heike
Jun 22, 2012 at 12:42
$\begingroup$ Thanks, but only the first method worked for me $\endgroup$
– Eddy
Jun 22, 2012 at 13:25

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