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Diffstat (limited to 'tests/examplefiles/idl_sample.pro')
| -rw-r--r-- | tests/examplefiles/idl_sample.pro | 73 |
1 files changed, 73 insertions, 0 deletions
diff --git a/tests/examplefiles/idl_sample.pro b/tests/examplefiles/idl_sample.pro new file mode 100644 index 00000000..814d510d --- /dev/null +++ b/tests/examplefiles/idl_sample.pro @@ -0,0 +1,73 @@ +; docformat = 'rst' + +; Example IDL (Interactive Data Language) source code. + +;+ +; Get `nIndices` random indices for an array of size `nValues` (without +; repeating an index). +; +; :Examples: +; Try:: +; +; IDL> r = randomu(seed, 10) +; IDL> print, r, format='(4F)' +; 0.6297589 0.7815896 0.2508559 0.7546844 +; 0.1353382 0.1245834 0.8733745 0.0753110 +; 0.8054136 0.9513228 +; IDL> ind = mg_sample(10, 3, seed=seed) +; IDL> print, ind +; 2 4 7 +; IDL> print, r[ind] +; 0.250856 0.135338 0.0753110 +; +; :Returns: +; lonarr(`nIndices`) +; +; :Params: +; nValues : in, required, type=long +; size of array to choose indices from +; nIndices : in, required, type=long +; number of indices needed +; +; :Keywords: +; seed : in, out, optional, type=integer or lonarr(36) +; seed to use for random number generation, leave undefined to use a +; seed generated from the system clock; new seed will be output +;- +function mg_sample, nValues, nIndices, seed=seed + compile_opt strictarr + + ; get random nIndices by finding the indices of the smallest nIndices in a + ; array of random values + values = randomu(seed, nValues) + + ; our random values are uniformly distributed, so ideally the nIndices + ; smallest values are in the first bin of the below histogram + nBins = nValues / nIndices + h = histogram(values, nbins=nBins, reverse_indices=ri) + + ; the candidates for being in the first nIndices will live in bins 0..bin + nCandidates = 0L + for bin = 0L, nBins - 1L do begin + nCandidates += h[bin] + if (nCandidates ge nIndices) then break + endfor + + ; get the candidates and sort them + candidates = ri[ri[0] : ri[bin + 1L] - 1L] + sortedCandidates = sort(values[candidates]) + + ; return the first nIndices of them + return, (candidates[sortedCandidates])[0:nIndices-1L] +end + + +; main-level example program + +r = randomu(seed, 10) +print, r +ind = mg_sample(10, 3, seed=seed) +print, ind +print, r[ind] + +end
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