ts barrett's functions to nest and unnest data.tables

group_nest_dt.R

+# Define function to nest DT by group, and unnest.
+# these functions were written by TS Barrett in a document available at https://osf.io/f6pxw/download
+group_nest_dt <-function(dt, ..., .key = "data"){
+  stopifnot(is.data.table(dt))
+  
+  by <-substitute(list(...))
+  
+  dt <- dt[, list(list(.SD)), by = eval(by)]
+  setnames(dt, old = "V1", new = .key)
+  dt
+}
+
+unnest_dt <-function(dt, col, id){
+  stopifnot(is.data.table(dt))
+  
+  by <-substitute(id)
+  col <-substitute(unlist(col, recursive = FALSE))
+  
+  dt[, eval(col), by = eval(by)]
+}
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