Undefined columns selected when subsetting data frame

I have a data frame, str(data) to show more about my data frame the result is the following:

> str(data)
'data.frame':   153 obs. of  6 variables:
$ Ozone  : int  41 36 12 18 NA 28 23 19 8 NA ...
$ Solar.R: int  190 118 149 313 NA NA 299 99 19 194 ...
$ Wind   : num  7.4 8 12.6 11.5 14.3 14.9 8.6 13.8 20.1 8.6 ...
$ Temp   : int  67 72 74 62 56 66 65 59 61 69 ...
$ Month  : int  5 5 5 5 5 5 5 5 5 5 ...
$ Day    : int  1 2 3 4 5 6 7 8 9 10 ...

However, for example, when I want to subset the amounts of Ozone above 14 I use the following code which gives me an error:

>  data[data$Ozone > 14 ]

Error in [.data.frame(data, data$Ozone > 14) : undefined columns selected

You want rows where that condition is true so you need a comma:

data[data$Ozone > 14, ]