[R] Hash, variable names restriction

Jeff Newmiller jdnewmil at dcn.davis.ca.us
Fri Dec 19 09:49:22 CET 2014

df is the name of a function in base R. You have not provided a definition 
of sample data resembling your real data. In this case I suspect that the 
source of your problems is that df may not be what you think it is. 
Learning to use the "str" function may help you.

If df is a data frame containing a column called "city", then df$city is a 
vector. You don't need to convert it to a vector. Nor do you need to 
concatenate it with anything.

Note that hash tables may not be the best or only way to accomplish this. 
The data.table package offers data frames with binary search indexing that 
can be quite fast, particularly if you plan to do these lookups on large 
amounts of data.

Try reading 
for ideas on how to communicate your problems with R more clearly.

On Fri, 19 Dec 2014, email wrote:

> Hi:
> I have one million names of city and their population and want to make
> a hash so that by giving key = city, the hash function will return its
> population.
> I use the hash package in R as follows:
> h <- hash(c(as.vector(df$city)), c(as.vector(df$population)))
> But getting the following error:
> Error in assign(keys[[i]], values[[i]], envir = hash at .Data) :
>  variable names are limited to 10000 bytes
> How can it be solved?
> Thanks:
> John
> ______________________________________________
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> and provide commented, minimal, self-contained, reproducible code.

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