# multi-Operations on a matrix

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## multi-Operations on a matrix

 Hello everybody. I have this object           procedure property sensor_data              sensor_date 1    S_10     nord    626821.0 2002-09-30T00:00:00+0200 2     S_10     nord    626821.0 2002-12-05T00:00:00+0100 3    S_10     nord    626821.1 2008-07-31T00:00:00+0200 4  S_1000     nord    626496.8 2002-09-30T00:00:00+0200 5  S_1000     nord    626496.8 2002-12-05T00:00:00+0100 6  S_1000     nord    626496.9 2009-04-23T00:00:00+0200 7  S_1000     nord    626497.0 2009-11-10T00:00:00+0100 8     S_1     nord    626485.3 2002-09-30T00:00:00+0200 9    S_1     nord    626485.3 2002-12-05T00:00:00+0100 10    S_1     nord    626485.3 2003-02-07T00:00:00+0100 the third colomn (sensor_data) is a distance in meters. each distance has a date (sensor_date) for each row I would like to find the difference from the first distance (with the min date) and the distance. I know it's difficult to understand.. I give you an example: for the first procedure S_10 I should find the first distance based on the date: distance:    626821.0   with the date: 2002-09-30T00:00:00+0200 then I should do the difference between the current distance and the first distance: 626821.0 - 626821.0 = 0.0  626821.0 -  626821.0 = 0.0 626821.1 - 626821.0 = 0.1 Then I should do this also for the other procedures. I would like a resut like this:      procedure property sensor_data              sensor_date     difference 1    S_10     nord    626821.0 2002-09-30T00:00:00+0200    0.0 2     S_10     nord    626821.0 2002-12-05T00:00:00+0100   0.0 3    S_10     nord    626821.1 2008-07-31T00:00:00+0200   0.1 4  S_1000     nord    626496.8 2002-09-30T00:00:00+0200  0.0 5  S_1000     nord    626496.8 2002-12-05T00:00:00+0100   0.0 6  S_1000     nord    626496.9 2009-04-23T00:00:00+0200    0.1 7  S_1000     nord    626497.0 2009-11-10T00:00:00+0100   0.2 8     S_1     nord    626485.3 2002-09-30T00:00:00+0200     0.0 9    S_1     nord    626485.3 2002-12-05T00:00:00+0100      0.0 10    S_1     nord    626485.3 2003-02-07T00:00:00+0100     0.0 How can I do this procedure????? Thanks