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:Well, algorithms I and III only scan the list of data once, whereas both versions of algorithm II scan it twice. Hence, since I/O is by several orders of magnitude slower than calculations, that means that, unless the whole data set is read into memory, algorithm II will be twice as slow, and it won't work if the data file is not seekable. --[[User:Army1987|Army1987]] 16:00, 28 October 2007 (UTC)
The Welford algorithm *is* an on-line algorithm, because it needs to see only one data item at a time! It does *not* need to store the complete set of data, i.e., it does not need to look at any data item more than once. <small><span class="autosigned">— Preceding [[Wikipedia:Signatures|unsigned]] comment added by [[User:Snoopy67|Snoopy67]] ([[User talk:Snoopy67|talk]] • [[Special:Contributions/Snoopy67|contribs]]) 21:30, 17 July 2011 (UTC)</span></small><!-- Template:Unsigned --> <!--Autosigned by SineBot-->
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