# What does the "<<-" operator mean?

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## What does the "<<-" operator mean?

 I've been reading some code from an example in a blog post (here) and I came across an operator that I hadn't seen before.  The author used a <<- operator to update a variable, like so: ecov_xy <<- ecov_xy+decay*(x[t]*y[t]-ecov_xy) At first I thought it was a mistake and tried replacing it with the usual <- assignment operator, but I didn't get the same results.  So what does the double arrow <<- operator do?
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## Re: What does the "<<-" operator mean?

 I should probably point out that in the example, "ecov_xy " and "decay" are scalars, and x and y are vectors.
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## Re: What does the "<<-" operator mean?

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## Re: What does the "<<-" operator mean?

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## Re: What does the "<<-" operator mean?

 In reply to this post by Cliff Clive On Apr 21, 2011, at 2:08 PM, Cliff Clive wrote: > I've been reading some code from an example in a blog post ( > http://www.maxdama.com/ here ) and I came across an operator that I hadn't > seen before.  The author used a <<- operator to update a variable, like so: > > ecov_xy <<- ecov_xy+decay*(x[t]*y[t]-ecov_xy) > > At first I thought it was a mistake and tried replacing it with the usual <- > assignment operator, but I didn't get the same results.  So what does the > double arrow <<- operator do? > It is a "super assignment" operator, which means that the assignment is done in the global environment, rather than to a variable that is within a function and therefore may only have local scope. This is covered a bit in "An Introduction To R":   http://cran.r-project.org/doc/manuals/R-intro.html#Assignment-within-functionsand a bit more in:  ?"<-" or  ?"<<-" It can be a bit hazardous to use, given the potential confusion over variable scoping issues, which is why <- and <<- may not be interchangeable as you are observing. HTH, Marc Schwartz ______________________________________________ [hidden email] mailing list https://stat.ethz.ch/mailman/listinfo/r-helpPLEASE do read the posting guide http://www.R-project.org/posting-guide.htmland provide commented, minimal, self-contained, reproducible code.
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## Re: What does the "<<-" operator mean?

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## Re: What does the "<<-" operator mean?

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