require(RPostgreSQL)
drv = dbDriver("PostgreSQL")
con = dbConnect(drv, host = ..., post =..., dbname =..., user=..., password=...)
df = dbGetQuery(con, query_string)
dbDisconnect(con)

df = data.frame(id = c(1:100), arrcol = c(rep(paste0("{{",paste0(1:99,collapse=","),"}}"),10)))

df$arrcol = gsub(fixed=T, "{", "", df$arrcol)
df$arrcol = gsub(fixed=T, "}", "", df$arrcol)

# Attempt 1:
df$arrcol = as.numeric(df$arrcol)
# Error: (list) object cannot be coerced to type 'double'

# Attempt 2:
df$arrcol = lapply(df$arrcol, function(x) strsplit(x, ",", fixed=T))
# no error, but now the data appears to be stored as a list of character lists:
# arrcol[1]: list(c("1", "2", "3", "4", "5",...

# Attempt 3:
df$arrcol = lapply(df$arrcol, function(x) as.numeric(unlist(strsplit(x, ",", fixed=T))))
# this one seems to work

df$arrcol = lapply(df$arrcol, function(x) as.numeric(unlist(strsplit(x, ",", fixed=T))))