remove old messages from topic

edit

I skipped all the messages which are older than 1 second. Here are excerpts from a python class:

def callback_laserscan(self, msg):
    # skip messages which older then 1 sec
    msg_secs = msg.header.stamp.secs
    now = rospy.get_time()
    if (msg_secs + 1 < now):
        return
   ...process new messages...

Here is how I subscribe to the topic:

self.sub = rospy.Subscriber('kobuki/laser/scan', LaserScan, self.callback_laserscan)

And the LaserScan message has a Header (std_msgs/Header):

uint32 seq
time stamp
string frame_id

Where the "stamp" field type is "time" which has a "secs" field with seconds since epoch. rospy.get_time() also returns with seconds so I could decide if the messages are new enough.

This worked for me in a simple case during the first/second day of learning ROS, but I do not know, if it is good/robust enough (probably not), so use it "as is".

If you're using roscpp, you can use a callback with the MessageEvent type and ignore messages received too far in the past:

void callback(const ros::MessageEvent<geometry_msgs::Twist>& event)
{
  const std::string& publisher_name = event.getPublisherName();
  ros::Time receipt_time = event.getReceiptTime();

  ROS_INFO("Got a msg at time %f from publisher: %s",
           receipt_time.toSec(), publisher_name.c_str());

  // Compare receipt_time with ros::Time::now() to ignore too old messages

  const geometry_msgs::Twist::ConstPtr msg = event.getConstMessage();
}