CODEWITHSUNDEEP
rdata.table
冷雨夜客
冷雨夜客

Reputation: 1

how to compute by row of data.table

I am now using the package data.table,however,I can barely find the way to compute by rows. for example :

apply(x,1,sum) # suppose x is a data.frame with many columns

Is there anyone who knows how to do this?

Upvotes: 0

Views: 1208

Answers (2)

dwong2107
dwong2107

Reputation: 9

You could try using transform(). For example, using a dummy dataset that I have:

> head(data)
   sample     time.min       abs time.sec
1:  pur n 0.0008333334 0.4678054     0.05
2:  pur n 0.2508333325 0.4661632    15.05
3:  pur n 0.5008333325 0.4663149    30.05
4:  pur n 0.7508333325 0.4658490    45.05
5:  pur n 1.0008333920 0.4671631    60.05
6:  pur n 1.2508333920 0.4657932    75.05

Let's say I want to sum the two "time" columns together, and fill a new column with that value. I could use transform() to do that:

> transform(data, time.sum = time.min + time.sec)
        sample     time.min       abs time.sec     time.sum
  1:     pur n 0.0008333334 0.4678054     0.05   0.05083333
  2:     pur n 0.2508333325 0.4661632    15.05  15.30083328
  3:     pur n 0.5008333325 0.4663149    30.05  30.55083328
  4:     pur n 0.7508333325 0.4658490    45.05  45.80083328
  5:     pur n 1.0008333920 0.4671631    60.05  61.05083691

Upvotes: 0

eddi
eddi

Reputation: 49448

Do your best to avoid by-row operations, but if you must:

dt[, your.by.row.operation, by = 1:nrow(dt)]

Upvotes: 2

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