lag

I'm making a very simple pong game in java and I'm doing this using KeyListener. I want it so when the user presses the right or left keys on the keypad, the pong block goes in that direction. This is a simple enough task, but what I'm finding out is that when the user holds down the key, the block moves once, stops for a short time, then continues moving until the user releases the key. I notice this happens when you try to hold down a letter key on a computer. If I try to hold down the 'a' key, the computer will do: a [pause] aaaaaaaaaaaaaaaa Is there someway to disable this stutter, because

In R, let's say I have this data frame: Data id date value 2380 10/30/12 21.01 2380 10/31/12 22.04 2380 11/1/12 22.65 2380 11/2/12 23.11 20100 10/30/12 35.21 20100 10/31/12 37.07 20100 11/1/12 38.17 20100 11/2/12 38.97 20103 10/30/12 57.98 20103 10/31/12 60.83 And I want to subtract the previous value from the current value, by group ID date, to create this: id date value diff 2380 10/30/12 21.01 0 2380 10/31/12 22.04 1.03 2380 11/1/12 22.65 0.61 2380 11/2/12 23.11 0.46 20100 10/30/12 35.21 0 20100 10/31/12 37.07 1.86 20100 11/1/12 38.17 1.1 20100 11/2/12 38.97 0.8 20103 10/30/12 57.98 0 20103