interpolation - How to use R interp1 similarly as MATLAB's? -

i trying interpolate linearly in r. pseudocode u = interp1(u, linspace(1, numel(u), numel(u)-1)); in matlab extrapolation returns nan if point outside domain (default, more here).

• approx rule=1 equivalent matlab pseudocode

i not sure second interp1 parameter not required in matlab let unsuccessufully y <- x such

interp1(x, y, xi, method = "linear") 

minimal code example (real 1 has > 500 k points linear work) , output @ top

list of 2  $ : num [1:3] 1 2 3  $ : num [1:2] 1 2  num [1:2] 0 1 error in interp1(x, y, xi, method = "linear") :    points 'xi' outside of range of argument 'x'. execution halted  library("pracma") # http://finzi.psych.upenn.edu/library/pracma/html/interp1.html  files <- vector("list", 2) files[[1]] <- c(1,2,3) files[[2]] <- c(1,2) str(files)  # wanted, matlab:  u = interp1(u, linspace(1, numel(u), numel(u)-1));  xi <- seq(0,1, len = length(files[[1]]) - 1) x <- files[[1]] y <- files[[1]] str(xi)  files[[1]] <- interp1(x, y, xi, method = "linear")  str(files) 

i know thread using interp1 in r matrix not have matrix.

input: c(1,2,3)
expected output: [1:2] datastructure

r: 3.3.1
os: debian 8.5

if you're willing na values on extrapolation, as default linear interpolation/extrapolation in interp1, approx() works fine:

files <- list(1:3,1:2) xi <- seq(0,1, len = length(files[[1]]) - 1) x <- files[[1]] y <- files[[1]] <- approx(x,y,xi) 

you said wanted two-element vector presumably want output y-values:

a$y ## [1] na  1 

this may seem wrong, correct answer question posed. you've used files[[1]] both x , y, approx() should return y=x when input in range 1 3, , na otherwise. in case xi [0 1], first element out of range of x/y data provided ...

ps can appreciate wanting use pracma similarity matlab's syntax, - although pracma high-quality , used - base r functions more used/thoroughly tested ...