How do I deal with this weird error function using dcast?

Question

I am using dcast in order to widen my data table:

df <- dcast(setDT(dt),locus ~ Indiv,value.var = 'x')

I have a data table that is 1254840 observations and 3 variables, I need to make it 3270 observations and 373 variables.

But every time I try to use the above function this error pops up:

Error in forderx(x, cols, sort=true, retgrp = false) :
 Failed to alloc cradix_counts

I think it is a memory issue but I cant find a way to get it to work, I have used gc(), and memory.limit() to no avail.

Is there anything I can do to combat this error or is there another way to widen my data table?