[datatable-help] melt spread

[Bacou, Melanie]

Carl,
Have you look into the data.table::dcast function to reshape tables from 
long to wide formats? See e.g. 
ftp://cran.r-project.org/pub/R/web/packages/data.table/vignettes/datatable-reshape.html 


--Mel.


On 1/17/2017 8:27 PM, Carl Sutton wrote:
> Hi
>
> This question is for information, not a coding problem.
>
> Basic information:
> The data table I am attempting to melt has 363 columns and 85,074 rows 
> (246.5MB).  The first 14 are id variables and pose no problem.  One of 
> the measure vars has sequences of 2:9,  The other 34 have sequence of 
> 1:10.   think paste0("var_",1:10)
>
> What works:
> It is a simple matter to melt these measure var columns using columns 
> 15:363.   Thanks to an answer on a prior question I can use tstrsplit 
> to split the sequence number off the column heading,   So far, so good.
>
> The difficulty:
> The problems arises when I attempt to spread the variable column which 
> contains prior column names sans sequence numbers.   I have searched 
> but not found a data.table function to spread the contents of 
> "variable" into separate columns.  The tidyr "spread" command maxes 
> out my available memory of 12GB.  I have attempted to use patterns to 
> melt into separate columns but that results in column names of valuex, 
> not the original column name.  In searching the arguments for melt I 
> have not seen one for preserving the original column names.  Perhaps I 
> missed something?
>
> The solution:
> Am I stuck with either
>     a) splitting my data.table such that tidyr does not max out 
> available memory, or
> b)  use set names on 35 columns to get viable column names?
>  Any and all thoughts are appreciated.  I have 20 of these datasets to 
> mung and am starting on one of the smaller ones.  The goal is write 
> the code once and use it on all datasets.
>
> Carl Sutton
>
>
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