outcome <- "Hospital.30.Day.Death..Mortality..Rates.from.Heart.Attack" #my column name variable
singlemetric[outcome] #returns the column using the variable
min(singlemetric$Hospital.30.Day.Death..Mortality..Rates.from.Heart.Attack,na.rm = TRUE) #this works

min(singlemetric$outcome,na.rm = TRUE) # this returns inf no non-missing arguments to min; returning Inf
min(singlemetric$[outcome],na.rm = TRUE) #also doesn't work Error: unexpected '[' in min(singlemetric$["