st: A precision problem

[Ronnie Babigumira <rb.glists@gmail.com>]

Dear List

My setup is Stata 10, winxp

I am "cleaning" some household data and I would like to identify cases where the product of quantity (cinp_qtry) and 
price (cinp_unpx) is not equal to the total cost (cinp_totcost) as entered in the data.

The data look something like this

    houscode   cinp_qty   cinp_unpx   cinp_totcost
          34          3          .6            1.8
          69          3          .6            1.8
          70          3          .6            1.8
          75          6          .6            3.6
          97          3          .6            1.8
         100          6          .6            3.6
         103          3           1             90

My first take was

- list houscode cinp_qty cinp_unpx cinp_totcost if cinp_totcost ! = (cinp_qty * cinp_unpx) -

    houscode   cinp_qty   cinp_u~x   cinp_t~t
           1          5         .6          3  <--------
          34          3         .6        1.8
          54          5         .6          3
          69          3         .6        1.8
          70          3         .6        1.8
          75          6         .6        3.6
          90          5         .6          3


When this caught the 3, I changed it to

list houscode cinp_qty cinp_unpx cinp_totcost if cinp_totcost ! = float(cinp_qty * cinp_unpx)

This improved things a bit however, the 1.8's were still caught.

    houscode   cinp_qty   cinp_u~x   cinp_t~t
          34          3         .6        1.8
          69          3         .6        1.8
          70          3         .6        1.8
          75          6         .6        3.6
          97          3         .6        1.8
         100          6         .6        3.6
         103          3          1         90

I then decided to first generate a new variable which I called pc_totcost computed as

gen float pc_totcost = cinp_qty * cinp_unpx

Then I issued

list  househd houscode  cinp_qty  cinp_unpx cinp_totcost pc_totcost if  ///
cinp_totcost !=  float(pc_totcost)


    houscode   cinp_qty   cinp_unpx   cinp_totcost   pc_totcost
          34          3          .6            1.8          1.8
          69          3          .6            1.8          1.8
          70          3          .6            1.8          1.8
          75          6          .6            3.6          3.6
          97          3          .6            1.8          1.8
         100          6          .6            3.6          3.6
         103          3           1             90            3 <----- this is the only "bug"
          70          3          .6            1.8          1.8
          70          3          .6            1.8          1.8
          97          3          .6            1.8          1.8
          97          3          .6            1.8          1.8
         100          6          .6            3.6          3.6

The 1.8's and 3.6's are "ok" to me. How can I get Stata to ignore them

Ronnie
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