Hi,

I was trying to query only a single age-sex group using a local SQL database. In getPopSql() here: https://github.com/wpgp/wopr/blob/master/R/getPopSql.R#L73 the code collapses to a vector when agesex_select has a length of 1 (e.g. 'm0'). If you add the option drop = FALSE to the data frame that will preserve the 2 dimensional structure that apply expects. Happy to submit a quick pull request with the change, if you'd like.