I'd need a function that checks my data frame for an otherwise identical row, but with date minus 1, and returns `true` if it exists. It's a large data frame, so I'd like to do it as efficiently as possible.

For example, take the following data frame:

```
name  |date       
Timmy |01/Jan/2016
Timmy |02/Jan/2016
Timmy |03/Jan/2016
Sally |04/Jan/2016
Johnny|13/Feb/2016
Johnny|29/Mar/2016

```

The function should see `Timmy|02/Jan/2016`, check if `Timmy|01/Jan/2016` exists, and return `true`. The resulting data frame would look like this:

```
name  |date       |hasDateMinusOne
Timmy |01/Jan/2016|false
Timmy |02/Jan/2016|true
Timmy |03/Jan/2016|true
Sally |04/Jan/2016|false
Johnny|13/Feb/2016|false
Johnny|29/Mar/2016|false

```

[This is the closest answer I've found.](https://stackoverflow.com/questions/5916854/existing-function-for-seeing-if-a-row-exists-in-a-data-frame) Although it was answered by Hadley, it's 5 years old and predates dplyr. I'm wondering if it's still the most efficient way to handle 1,000,000+ rows.

Thanks!

Sean