Using data.table syntax to update column

Question

I have a data.table DT with 2 columns: ID, QTY

     ID        QTY
    000001       0
    000002       1
    000002       2
    000004       0
    000005       1
    000006       2

I want to update the Qty column for those rows where Qty is greater than 1 and replace the corresponding Qty value with 1. This is a trivial task that can be performed by using sapply or simply using which command on the column. But I want to know if this can be achieved using the data.table[i,j,by/keyby,.SD] options.

Expected Output:

     ID        QTY
    000001       0
    000002       1
    000002       1
    000004       0
    000005       1
    000006       1

akrun · Accepted Answer · 2017-01-25 08:37:14Z

3

We can do this by converting the logical vector to binary with as.integer

DT[, QTY := as.integer(QTY>0)]
DT
#   ID QTY
#1:  1   0
#2:  2   1
#3:  2   1
#4:  4   0
#5:  5   1
#6:  6   1

Or specify it in the i and update the 'QTY'

DT[QTY>0, QTY := 1]

answered Jan 25, 2017 at 8:37

akrun

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5 Comments

tushaR Over a year ago

does this operator ":=" has a special name? I could not find it in the vignette for introduction to data.table.

akrun Over a year ago

@Tushar It is the assignment operator

tushaR Over a year ago

@DavidArenburg Will check this out too. Thanks a lot.

Emman Over a year ago

@DavidArenburg the link is broken.

David Arenburg Over a year ago

@Emman cran.r-project.org/web/packages/data.table/vignettes/…

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