I need to create the sum of next 7 days values of a column in r.The sum should be grouped by another column which has string values

Example

```
name   value 
a       2    
a       3  
a       3  
b       4  
b       3  
b       2  
b       1  
b       3  

```

sum by 2 next rows 

output

```
sum
5
6
3
7
5
3     
4
3

```