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May 11, 2011 7:11 PM
(7318 views)

I can use summary to find the maximums (multiple due to groups) in one column. However, I also want to look up in which rows in the original table the maximums occur.

Is there an easy solution? Thanks for your help!

Is there an easy solution? Thanks for your help!

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I know this is two years later, but this is for all those who found this post with the same question.

Try the function "Get Selected Rows" in your script.

```
yourarray = dt << Get Selected Rows;
```

Now the array "yourarray" will contain a list of the row numbers that are selected.

To find the rows with the maximum value, try

```
// finds the maximum value in the columnt
peakvalue = Col Max( :columname);
// selects all rows with the maximum value. (dt is the name of the data table.)
dt << Select Where( :columnname == peakvalue);
// stores a list of the row numbers with the maximum value in this array
yourarray = dt << Get Selected Rows;
```

11 REPLIES

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Re: Select rows with maximal values in one column

You can match the original table with the summary table using Update (Tables menu) with group column(s) = group column(s) and data = max(data) as matching columns. The maximum rows will be denoted by non-missing cells in the added NRows column.

My first answer was based on sloppy thinking...

Message was edited by: MS

My first answer was based on sloppy thinking...

Message was edited by: MS

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Re: Select rows with maximal values in one column

MS,

Thanks. I gave it a try and I am still selecting all rows in the original table when selecting the 2nd summary table. Whenever I select one row (Max for the group) in the summary table, every row in the first summary table in the group also gets selected.

I hope I am following your instruction correctly. Is the 2nd summary table named as "DataTable By (group, data) By (group)" ?

FYI, I am using JMP7.

Dong

Thanks. I gave it a try and I am still selecting all rows in the original table when selecting the 2nd summary table. Whenever I select one row (Max for the group) in the summary table, every row in the first summary table in the group also gets selected.

I hope I am following your instruction correctly. Is the 2nd summary table named as "DataTable By (group, data) By (group)" ?

FYI, I am using JMP7.

Dong

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Re: Select rows with maximal values in one column

Sorry, you´re right. I was too quick to answer. I will edit my erroneous post above

What I wanted to suggest is that you can try to combine Summary with Update (or Join, I am not sure Update is found in the JMP7 Tables Menu).

Here's a script example that should work but may be ineffective for very large data tables.

```
dt = Open( "$SAMPLE_DATA/Big Class.jmp" );
dt << clear select;
Summarize( g = by( :sex ), m = Max( :age ) );
For( j = 1, j <= N Items( g ), j++,
For Each Row( If( :sex == g[j] & :age == m[j], Row State() = Selected State( 1 ) ) )
);
```

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Re: Select rows with maximal values in one column

The script looks good. I will give it a try and report back.

What surprised me is that JMP itself does not keep the index (row number) of the data maximum somewhere.

Dong

What surprised me is that JMP itself does not keep the index (row number) of the data maximum somewhere.

Dong

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Re: Select rows with maximal values in one column

For Each Row() can be inefficient for large tables.

Select Where() will probably be faster:

```
dt = Open( "$SAMPLE_DATA/Big Class.jmp" );
dt << clear select;
Summarize( g = by( :age ), m = Max( :height ) );
dt<<Select Where(:height==m[loc(g,char(:age) )]);
```

-Jeff

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Re: Select rows with maximal values in one column

Fantastic solution. This is exactly what I was looking for!

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Re: Select rows with maximal values in one column

I got JMP10 and revisited this problem. "Join" using column matching works well. I guess table "update" seems would be even more straightforward.

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Re: Select rows with maximal values in one column

Rows->Row Selection->Select Dominant will select the rows with the maximum (or minimum) values in a column or group of columns.

I believe that'll get you what you're looking for.

Jeff

I believe that'll get you what you're looking for.

Jeff

-Jeff

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Re: Select rows with maximal values in one column

May 12, 2011 10:43 AM
(5649 views)
| Posted in reply to message from Jeff_Perkinson 05/12/2011 09:55 AM

Jeff,

Thanks. This appears to be new feature from JMP 9. I am using JMP 7. I guess I may request an upgrade.

Also, I am trying to select multiple maximums in one column. The maximums belong to different groups specified in other columns.

Dong

Thanks. This appears to be new feature from JMP 9. I am using JMP 7. I guess I may request an upgrade.

Also, I am trying to select multiple maximums in one column. The maximums belong to different groups specified in other columns.

Dong