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- Syntax: How do I create an index column by ID

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Oct 7, 2014 6:35 AM
(10160 views)

Hello JMP Community,

I am trying to create a column that indexes rows by an ID column.

In other scripting language, this is accomplished with the following lines.

By ID: gen IDIndex = _n

By ID: gen IDCount = _N

I can do the following, but I index and count the whole table

New Column( "IDIndex",

formula(Row()));

New Column( "IDCount",

formula(NRow()));

Advice on this would be great!

Very Sincerely,

ID | IDIndex | IDCount |
---|---|---|

444 | 1 | 4 |

444 | 2 | 4 |

444 | 3 | 4 |

444 | 4 | 4 |

333 | 1 | 3 |

333 | 2 | 3 |

333 | 3 | 3 |

1 ACCEPTED SOLUTION

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In your formula you need to check the ID value to see if it has changed from the previous row and reset your index if it has.

Try this formula:

If(:ID != Lag(:ID, 1) | Row() == 1, 1, Lag(:IDIndex, 1) + 1)

Your ID Count column has use IDIndex to get its value:

Col Maximum( :IDIndex, :ID )

The second argument to the Col Maximum function is the By variable.

I hope that helps!

-Jeff

-Jeff

5 REPLIES

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In your formula you need to check the ID value to see if it has changed from the previous row and reset your index if it has.

Try this formula:

If(:ID != Lag(:ID, 1) | Row() == 1, 1, Lag(:IDIndex, 1) + 1)

Your ID Count column has use IDIndex to get its value:

Col Maximum( :IDIndex, :ID )

The second argument to the Col Maximum function is the By variable.

I hope that helps!

-Jeff

-Jeff

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Oct 7, 2014 7:40 AM
(9612 views)
| Posted in reply to message from Jeff_Perkinson 10/07/2014 10:25 AM

Great, that worked perfectly!

Thanks for quick reply.

Have a great day,

Matt

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Jeff is correct and i will only add that the formula for IDIndex depends on previous sorting.

If the table needs to be re-sorted later you would need to suppress evaluation or delete it.

column (dt, "IDIndex") << suppress eval ( true );

or:

column (dt, "IDIndex") << delete formula;

to produce the column IDCount without sorting you can use the table summery option:

dt << Summary (Group ( :ID );

ron

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I think the below formula will work for IDIndex independently of the initial sorting of the ID column:

Sum( :ID[Index( 1, Row() )] == :ID )

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Thanks MS, the command you shared does work independently of the sorting.

Have a great day!