Generated percent variable not rounding properly

[Lexi Mastalerz]

Hello,

I generated a float variable of a percentage:


g double share = weeks/tbw if fs==0
replace share = round(share, 0.1)
replace share = share*100

Dataex input:

clear
input float(fs weeks) int tbw float fam_inc double share
1 . 20 30295 .
1 . 19 30295 .
1 . 50 34752 .
0 3 30 25528 10
0 4 40 23408 10
1 . 24 31911 .
1 . 43 31798 .
0 17 50 15625 30.000000000000004
0 14 29 10581 50
1 . 15 35026 .
1 . 35 38734 .
1 . 18 27337 .
0 12 42 8673 30.000000000000004
0 13 13 21922 100
0 50 50 18412 100
1 . 20 31228 .
1 . 14 27775 .
0 3 37 19436 10
1 . 22 26442 .
1 . 27 26661 .
1 . 38 26661 .
1 . 27 29479 .
0 21 21 720 100
1 . 73 31693 .
0 39 50 13459 80
1 . 27 34868 .
1 . 23 34868 .
0 9 9 1 100
0 18 30 19989 60.00000000000001
1 . 20 29150 .
end
[/CODE]

I don't know why the 30% and 60%, is not rounded, but shows up as 60.0000000001.

When I don't do a double, strange things are happening as well. It doesn't show up like that but I cant browse if I say "br if share==60".

Thanks!

[Maarten Buis]

This is a precision problems, as I suppose you guessed wenn creating the variables explicitly as doubles. The problem is that 1/10 in binary is 0.111111111111111 etc. so it has to be rounded. The easiest sollution is first multiply by a 100 and than round to the closest multiple of 10, as 10 is a numer with a exact representation in binary (1010), so it does not have to be rounded.

gen double share = weeks/tbw if fs==0
replace share = share*100
replace share = round(share, 10)

[Lexi Mastalerz]

Thank You