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### 10.8 Examples

Here are some examples for defining new columns; the expressions below could appear as the `<expr>` in a `tpipe` `addcol` or `sortexpr` command).

Average

         (first + second) * 0.5

Square root

         sqrt(variance)

Angle conversion

         radiansToDegrees(DEC_radians)
         degreesToRadians(RA_degrees)

Conversion from string to number

         parseInt($12)
         parseDouble(ident)

Conversion from number to string

         toString(index)

Conversion between numeric types

         toShort(obs_type)
         toDouble(range)

  or

         (short) obs_type
         (double) range

Conversion from sexagesimal to degrees

         hmsToDegrees(RA1950)
         dmsToDegrees(decDeg,decMin,decSec)

Conversion from degrees to sexagesimal

         degreesToDms($3)
         degreesToHms(RA,2)

Outlier clipping

         min(1000, max(value, 0))

Converting a magic value to null

         jmag == 9999 ? NULL : jmag

Converting a null value to a magic one

         NULL_jmag ? 9999 : jmag

Taking the third scalar element from an array-valued column

         psfCounts[2]

Converting spectral type to numeric value (e.g. "L3.5" -> 23.5, "M7" -> 17)

         "MLT".indexOf(spType.charAt(0)) * 10 + parseDouble(substring(spType,1)) + 10

  Note this uses a couple of Java String instance methods (Section 10.9.2) which are not explicitly documented in this section.

Here are some examples of boolean expressions that could be used for row selection (appearing in a `tpipe` `select` command)

Within a numeric range

         RA > 100 && RA < 120 && Dec > 75 && Dec < 85

Within a circle

         $2*$2 + $3*$3 < 1
         skyDistanceDegrees(ra0,dec0,hmsToDegrees(RA),dmsToDegrees(DEC))<15./3600.

First 100 rows

         index <= 100

  (though you could use `tpipe cmd='head 100'` instead)
Every tenth row

         index % 10 == 0

  (though you could use `tpipe cmd='every 10'` instead)
String equality/matching

         equals(SECTOR, "ZZ9 Plural Z Alpha")
         equalsIgnoreCase(SECTOR, "zz9 plural z alpha")
         startsWith(SECTOR, "ZZ")
         contains(ph_qual, "U")

String regular expression matching

         matches(SECTOR, "[XYZ] Alpha")

Test for non-blank value

         ! NULL_ellipticity

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STILTS - Starlink Tables Infrastructure Library Tool Set
Starlink User Note256
STILTS web page: http://www.starlink.ac.uk/stilts/
Author email: m.b.taylor@bristol.ac.uk
Mailing list: topcat-user@jiscmail.ac.uk