###### Vérification du nombre d'observations par année
verif_africa=data.frame(year=1901:2012,nb_obs=NA)
verif_asia=data.frame(year=1901:2012,nb_obs=NA)
verif_eur=data.frame(year=1901:2012,nb_obs=NA)
verif_NoAm=data.frame(year=1901:2012,nb_obs=NA)
verif_SoAm=data.frame(year=1901:2012,nb_obs=NA)
verif_oceana=data.frame(year=1901:2012,nb_obs=NA)

j=1
for (i in 1901:2012){
  afr=subset(africa.data,africa.data$year==i)
  verif_africa[j,]$nb_obs=dim(afr)[1]
  
  asi=subset(asia.data,asia.data$year==i)
  verif_asia[j,]$nb_obs=dim(asi)[1]
  
  eur=subset(eur.data,eur.data$year==i)
  verif_eur[j,]$nb_obs=dim(eur)[1]
  
  NoA=subset(NoAm.data,NoAm.data$year==i)
  verif_NoAm[j,]$nb_obs=dim(NoA)[1]
  
  SoA=subset(SoAm.data,SoAm.data$year==i)
  verif_SoAm[j,]$nb_obs=dim(SoA)[1]
  
  ocea=subset(oceana.data,oceana.data$year==i)
  verif_oceana[j,]$nb_obs=dim(ocea)[1]
  j=j+1
}