df <- iris
df$isfit <- ifelse(df$Species=='setosa',"Fit","Unfit")
table(df$isfit)
# Fit Unfit
# 50 100
# so only 33% are really fit
sampled_df_index <- sample(x=1:nrow(df),
size=200,
replace=TRUE,
prob = ifelse(df$isfit=="Fit",6,1))
sampled_df <- df[sampled_df_index,]
table(sampled_df$isfit)