JSL: Initialize column with an array 1 to N Rows()

Question

Hi,

this should be very easy but I just can't get the trick.

I want to create in a datatable a new column with a data sequence from 1 to number of rows in this table. I know the set Initial data command and also the set values command. Even I thought about using a Matrix. But I do not want to manually create the sequence.

Isn't there a way to say I want an Array from 1 to 10 by simply typing something like [1:10] or Sequence(1,10, 1) (I noticed sequence command does something different, but I hope you get the message).

Thanks for your help,

Martin

martindemel · Answer

Thanks to Bernd, Stan and Brady!!!

Now I have the challenge to choose

I like the simplier the better, so the "set values" command is my favorite. Especially with the "::" (double colon). This :: is exactly what I looked for to create an array, e.g. (1::10) will provide [1 2 3 4 5 6 7 8 9 10]. Thx a lot!!

brady_brady · Answer

If you don't need the flexibility of a loop or the sequence command, the <<set values message will run more quickly (an order of magnitude, in the example below.) Even column formulas which are subsequently deleted may run more quickly.

Run the script below to get a look at the timings for a 1M row table. In your particular case you could get by with the 3rd approach.

dt = astable(J(1e6,1,.));

t1 = hptime();

column(dt,1)<<Set Formula(Row());

dt << run formulas;

column(dt, 1) << Delete Formula;

print(hptime()-t1);

t2 = hptime();

for each row(

:Col 1 = Row()

);

print(hptime()-t2);

t3 = hptime();

column(dt,1)<<set values(1::nrow(dt));

print(hptime()-t3);

stan_koprowski · Answer

Martin,

You are on the right track...and a little more detail to expand on Bernd's example.

// Create a new data table

dt = New Table("Sequence Example");

// Add 2 columns and 50 rows

dt << New Column("Count to Twenty-Five", numeric);

dt << New Column("Count to Seventeen by Three" , numeric);

dt << Add Rows (50);

//  Sequence (start, end, by(optional), repeat(optional)

For Each Row (

column(1)[ ] = Sequence(1,25);

column(2)[ ] = Sequence(1,17, 3, 2);

);

// for matrix use index function // third argument is optional incrementer

// for each row will fill to end of table

For Each Row (

Column(1) << Set Values( Index(1, 25) );

Column(2) << Set Values( Index(1, 17, 3) );

);