python - NumPy indexing with varying position -


i have array input_data of shape (a, b, c), , array ind of shape (b,). want loop through b axis , take sum of elements c[b[i]] , c[b[i]+1]. desired output of shape (a, b). have following code works, feel inefficient due index-based looping through b axis. there more efficient method?

import numpy np  input_data = np.random.rand(2, 6, 10) ind = [ 2, 3, 5, 6, 5, 4 ]  out = np.zeros( ( input_data.shape[0], input_data.shape[1] ) )  in range( len(ind) ):     d = input_data[:, i, ind[i]:ind[i]+2]     out[:, i] = np.sum(d, axis = 1)

edited based on divakar's answer:

import timeit import numpy np  n = 1000  input_data = np.random.rand(10, n, 5000) ind = ( 4999 * np.random.rand(n) ).astype(np.int)  def test_1(): # old loop-based method     out = np.zeros( ( input_data.shape[0], input_data.shape[1] ) )      in range( len(ind) ):         d = input_data[:, i, ind[i]:ind[i]+2]         out[:, i] = np.sum(d, axis = 1)     return out  def test_2():      extent = 2 # comes 2 in "ind[i]:ind[i]+2"      m,n,r = input_data.shape     idx = (np.arange(n)*r + ind)[:,none] + np.arange(extent)     out1 = input_data.reshape(m,-1)[:,idx].reshape(m,n,-1).sum(2)     return out1  print timeit.timeit(stmt = test_1, number = 1000) print timeit.timeit(stmt = test_2, number = 1000)  print np.all( test_1() == test_2(), keepdims = true )  >> 7.70429363482 >> 0.392034666757 >> [[ true]]

here's vectorized approach using linear indexing broadcasting. merge last 2 axes of input array, calculate linear indices corresponding last 2 axes, perform slicing , reshape 3d shape. finally, summation along last axis desired output. implementation -

extent = 2 # comes 2 in "ind[i]:ind[i]+2"  m,n,r = input_data.shape idx = (np.arange(n)*r + ind)[:,none] + np.arange(extent) out1 = input_data.reshape(m,-1)[:,idx].reshape(m,n,-1).sum(2)

if extent going 2 stated in question - "... sum of elements c[b[i]] , c[b[i]+1]", -

m,n,r = input_data.shape ind_arr = np.array(ind) axis1_r = np.arange(n) out2 = input_data[:,axis1_r,ind_arr] + input_data[:,axis1_r,ind_arr+1]

Comments

Post a Comment

Popular posts from this blog

javascript - jQuery: Add class depending on URL in the best way -

i have html progress meter: <div class="col-md-3" style="margin-left: -20px;"> <div class="progress-pos active" id="progess-1"> <div class="progress-pos-inner"> login </div> </div> </div> <div class="col-md-3 progress-pos-container"> <div class="progress-pos" id="progess-2"> <div class="progress-pos-inner"> scan items </div> </div> </div> <div class="col-md-3 progress-pos-container"> <div class="progress-pos" id="progess-3"> <div class="progress-pos-inner"> confirm address </div> </div> </div> <div class="col-md-3 progress-pos-container"> <div class="progress-pos" id="progess-4"> <div class="progress-pos-in...
Read more

caching - How to check if a url path exists in the service worker cache -

i need check if particular url path exists in service worker cache. example, suppose url is: /myserviceworker/service?a=110&b=70 this url exists in cache, there many of them different values of , b. now, suppose want refresh of these urls, how can that? i want know how access key values service worker cache. if know key, plan follows: var url = new url(key); if(url.pathname === "\/myserviceworker/service") refetch key but not sure how cache key , in format is. mean, string or url? cache api has match() method returns promise resolving in response object if match or undefined if no match exists. second parameter object can specify ignoresearch not take account url parameters. the ignoresearch option supported firefox ( chrome status here ). in other hand, retrieve cache entries, can use keys() method.
Read more

Redirect to a HTTPS version using .htaccess -

i need modify .htaccess file redirect urls https version without "www". http://example.com --> https://example.com http://www.example.com --> https://example.com https://www.example.com --> https://example.com this how .htaccess file looks like: rewriteengine on rewritecond %{request_filename} !-d rewritecond %{request_filename} !-f rewriterule ^(.*)$ redirect.php?id=$1&page=$2 [qsa,l] what modifications need make .htaccess in order forward https without "www"? it depends on doing current code. looks file called redirect trying display php page seo friendly url. think might confusing people. anyway, need , force https without www, need 1 more rule above. also second rule needs two capture groups in rewriterule test string because wanting 2 different values using $1 , $2 references. rewriteengine on #rediect www non www and/or http https --- combinations. rewritecond %{http_host} !^example\.com [nc,or] rewritecond %{https} !^...
Read more