sample

Python has my_sample = random.sample(range(100), 10) to randomly sample without replacement from [0, 100) . Suppose I have sampled n such numbers and now I want to sample one more without replacement (without including any of the previously sampled n ), how to do so super efficiently? update: changed from "reasonably efficiently" to "super efficiently" (but ignoring constant factors) Chronial Note to readers from OP: Please consider looking at the originally accepted answer to understand the logic, and then understand this answer. Aaaaaand for completeness sake: This is the concept of

I'm trying to take out samples from two dataframes wherein I need the ratio of count maintained. eg df1.count() = 10 df2.count() = 1000 noOfSamples = 10 I want to sample the data in such a way that i get 10 samples of size 101 each( 1 from df1 and 100 from df2) Now while doing so, var newSample = df1.sample(true, df1.count() / noOfSamples) println(newSample.count()) What does the fraction here imply? can it be greater than 1? I checked this and this but wasn't able to comprehend it fully. Also is there anyway we can specify the number of rows to be sampled? Daniel de Paula The fraction

I have a large data.table (about 24000 rows and growing). I want to subset that datatable based on a couple of criteria and from that subset (ends up being about 3000 rows) I want to randomly sample just 4 rows. I do not want to create a named 3000 or so row data.table, count its rows and then sample based on row number. How can I do it on the fly? Or should I just suck it up by creating the table and then working on it, sampling it and then using rm() to get rid of it? Lets simulate my issue require(data.table) random.length <- sample(x = 15:30, size = 1) data.table(city=sample(c("Cape Town",

I'm using the MediaScannerConnection example code from the API Demos The snippet I'm using is: MediaScannerConnection.scanFile(context, new String[] { permFile.getAbsolutePath() }, null, new MediaScannerConnection.OnScanCompletedListener() { public void onScanCompleted(String path, Uri uri) { android.util.Log.i("ExternalStorage", "Scanned " + path + ":"); android.util.Log.i("ExternalStorage", "-> uri=" + uri); } }); When I run this code I get a FC dialog with the following from the LogCat: 4-20 23:17:45.988: ERROR/ActivityThread(3015): Activity com.my.package.name has leaked ServiceConnection

Why does the rdd.sample() function on Spark RDD return a different number of elements even though the fraction parameter is the same? For example, if my code is like below: val a = sc.parallelize(1 to 10000, 3) a.sample(false, 0.1).count Every time I run the second line of the code it returns a different number not equal to 1000. Actually I expect to see 1000 every time although the 1000 elements might be different. Can anyone tell me how I can get a sample with the sample size exactly equal to 1000? Thank you very much. If you want an exact sample, try doing a.takeSample(false, 1000) But note