t-test using OpenCPU

Question

I tried to use t-test in R using OpenCPU as follows -

<script src="//code.jquery.com/jquery-1.11.1.min.js"></script>
<script src="//cdn.opencpu.org/opencpu-0.4.js"></script>

and

ocpu.seturl("//public.opencpu.org/ocpu/library/stats/R")

var x = [1,2,3,4,5,6,7,8,9,10];
var y = [7,8,9,10,11,12,13,14,15,16,17,18,19,20];
// call R function: stats::t.test
var req = ocpu.rpc("t.test",{
    "x" : x,
    "y" : y
}, function(output){
    alert("t.test equals: " + output);
});

//optional
req.fail(function(){
    alert("R returned an error: " + req.responseText);
});

But I got this error

I am unable to understand where I am going wrong

I've never used that function or that calling convention but it appears that you failed to supply the second argument, namely "stats" that was expected. — IRTFM, Dec 21 '15 at 22:28
@42- I am not clear abour the "stats" argument.. I included the library in `ocpu.seturl("//public.opencpu.org/ocpu/library/stats/R") ` in the setup. Where else did I miss out? — Dinesh, Dec 21 '15 at 22:33
@Jeroen Thanks for the prompt reply. But is there any way we can get only the `p-value` for the t-test? In `R`, i know we can do it by `t.test(x,y)$p.value` ? — Dinesh, Dec 21 '15 at 22:37

Jeroen Ooms · Accepted Answer · 2015-12-22T10:40:34.933

The ocpu.rpc function is a shorthand that retrieves the output as JSON. However there is no JSON representation of a t.test object. Therefore you can use ocpu.call and retrieve e.g. the console output from the session [fiddle]:

var req = ocpu.call("t.test",{
    x : x,
    y : y
}, function(session){
  session.getConsole(function(outtxt){
      $("code").text(outtxt);
  });
});

If you want actual data (e.g p-value), I recommend you create an simple R package with a wrapper function that returns a list with data you are interested in:

my_ttest <- function(x, y){
  out <- t.test(x,y)
  list(
    n1 = length(x),
    n2 = length(y),
    p = out$p.value
  )
}

You will be able to call this function using ocpu.rpc as you did above, because the list can be mapped directly to JSON. Note that you can easily deploy your own package on the public demo server with the github webhook.

Hi thanks for the information. I created a package on github - now how can I call the function in the github package with opencpu? — Dinesh, Jun 10 '16 at 16:30
got it - `ocpu.seturl("//public.opencpu.org/ocpu/github/githubusername/packagename/R")` — Dinesh, Jun 10 '16 at 18:59

t-test using OpenCPU

1 Answers1