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Let's suppose I have a 3 by 5 matrix in R:
4 5 5 6 8
3 4 4 5 6
2 3 3 3 4
I would like to interpolate in between these values to create a matrix of size 15 by 25. I would also like to specify if the interpolation is linear, gaussian, etc. How can I do this?
For example, if I have a small matrix like this
2 3
1 3
and I want it to become 3 by 3, then it might look like
2 2.5 3
1.5 2.2 3
1 2 3
387
method:specifies the interpolation method to be used. Choices are “linear” or “constant”. n:If xout is not specified, interpolation takes place at n equally spaced points spanning the interval [min(x), max(x)]. yleft: the value to be returned when input x values are less than min(x).
approx returns a list with components x and y , containing n coordinates which interpolate the given data points according to the method (and rule ) desired. The function approxfun returns a function performing (linear or constant) interpolation of the given data points.
Interpolation means determining a value from the existing values in a given data set. Another way of describing it is the act of inserting or interjecting an intermediate value between two other values.
app <- function(x, n) approx(x, n=n)$y # Or whatever interpolation that you want
apply(t(apply(x, 1, function(x) app(x, nc))), 2, function(x) app(x, nr))
[,1] [,2] [,3]
[1,] 2.0 2.50 3
[2,] 1.5 2.25 3
[3,] 1.0 2.00 3
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