create sequence vector for each level of other column

Asked Nov 06 '15 at 19:06

Active Nov 06 '15 at 19:06

Viewed 38 times

I have a data table something like this. This is just a sample. col1 has a lot more levels

col1      col2
A          231
A          532
A          764
A          532
B          432
B          432
B          443
B          343 
B          643
B          322
B          334

What I want is the following

col1      col2      squence_per_col1
A          231           1 
A          532           2
A          764           3
A          532           4 
B          432           1
B          432           2 
B          443           3
B          343           4
B          643           5
B          322           6 
B          334           7

Basically I want to create sequence column for each level of col1 in a very efficient manner. Please not that this is a data.table. Please provide a solution with data table syntax.

How do I do it?

asked Nov 06 '15 at 19:06

user3664020

2,980
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1

Just use `sequence` and `.N` or `getanID` from my "splitstackshape" package. – A5C1D2H2I1M1N2O1R2T1 Nov 06 '15 at 19:08
1

`dt[,1:.N,col1]` and `getanID(dt, 'col1')[]` – Pierre L Nov 06 '15 at 19:13
1

or `dt[, rleid(col2), col1]` (which gives a slightly different effect) – Jaap Nov 06 '15 at 19:15

create sequence vector for each level of other column

0 Answers0