Checking if Lng and Lat fall inside polygons from ESRI Shape file

Question

I am trying this bit of code in R to check in which subzone does a particular latitude, longitude lie in. The idea is to loop all the subzone names and check in them, rather than a particular subzone( in Singapore).wa.map$SUBZONE_N gives the names of the subzones in Singapore. I am getting the following error in R:

Error in (function (classes, fdef, mtable) : unable to find an inherited method for function ‘proj4string<-’ for signature ‘"data.frame", "character"’

Please help me as to how I can do this.

wa.map <- readOGR("C:/Users/somna/Desktop/master-plan-2014-subzone-boundary-   no-sea-shp/MP14_SUBZONE_NO_SEA_PL.shp", layer="MP14_SUBZONE_NO_SEA_PL")
dat <- data.frame(Longitude = c(103.83838894560753,103.83636995885735),
              Latitude =c(1.27744837946643, 1.27734776750189),
              names = c("Blk 3", "Bef Hosp Dr"))

for (i in 1:323)
{
  sodo <- wa.map[wa.map$SUBZONE_N[i],]

  proj4string(dat) <- proj4string(sodo)

  over(sodo, dat)

}