[R] Comparison conditionals when extracting from data.frame not working reliably

[Ista Zahn]

Use & instead of &&

--Ista

On Sep 9, 2016 8:12 AM, "Matti Viljamaa" <mviljamaa at kapsi.fi> wrote:

> I’m getting strange behaviour when trying to extract rows from a
> two-column data.frame with double values.
>
> My data looks like:
>
>        mom_iq kid_score
> 1   121.11750        65
> 2    89.36188        98
> 3   115.44320        85
> 4    99.44964        83
> …
>
> and I’m testing extracting rows that have mom_iq at some interval, so e.g.
>
> kidmomiq[kidmomiq$mom_iq > 80.0 && kidmomiq$mom_iq < 130.0,]
>
> correctly returns rows that have mom_iq \in ]80.0, 130.0[.
>
> However, if I adjust this to:
>
> kidmomiq[kidmomiq$mom_iq > 80.0 && kidmomiq$mom_iq < 120.0,]
>
> (and there are clearly values that also fall \in ]80.0, 120.0[ !)
>
> I get:
>
> [1] mom_iq    kid_score
> <0 rows> (or 0-length row.names)
>
> Why does the extraction fail on some values, but not some others?
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