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Asked: 2026-05-30T13:44:24+00:00

Other posts suggested that ddply is a good workhorse. I am trying to learn

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Other posts suggested that ddply is a good workhorse.
I am trying to learn xxply functions and I can not solve this problem.

This is my 

library(ggplot2)
(df= tips[1:5,])
             total_bill                   tip    sex smoker day   time size
1 16.989999999999998437 1.0100000000000000089 Female     No Sun Dinner    2
2 10.339999999999999858 1.6599999999999999201   Male     No Sun Dinner    3
3 21.010000000000001563 3.5000000000000000000   Male     No Sun Dinner    3
4 23.679999999999999716 3.3100000000000000533   Male     No Sun Dinner    2
5 24.589999999999999858 3.6099999999999998757 Female     No Sun Dinner    4

and I need to something like this

ddply(df
       ,.(<do I have to enumerate all columns I need to operate on here?)>
       , function(x) {if size>=3 return(size) else return(total_bill+tip)
     )

(the example is a fake problem (does not make real life sense) and only demonstrates my problem with larger data)

  1. I could not get the ddply code right reading just help files. Any advise appreciated. Or even great ddply tutorial?

  2. I like that with ddply I can just pass my dataframe as input, but in the second argument, it is not nice that I am forced to enumerate all columns that I need later. Is there a way to pass the whole row (all columns)?

  3. I like defining the function on the fly, but I am not sure how to make my pseudocode correct in R (my last argument).

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1 Answer

  1. Editorial Team

    Based on your code, it doesn’t look like you need to use plyr here at all. It seems to me you are calculating a new variable for each row of the data.frame. If that’s the case, then just use some base R functions:

    dat <- transform(dat, newval = ifelse(size >= 3, size, total_bill + tip))

  total_bill  tip    sex smoker day   time size newval
1      16.99 1.01 Female     No Sun Dinner    2  18.00
2      10.34 1.66   Male     No Sun Dinner    3   3.00
3      21.01 3.50   Male     No Sun Dinner    3   3.00
4      23.68 3.31   Male     No Sun Dinner    2  26.99
5      24.59 3.61 Female     No Sun Dinner    4   4.00

    Sorry if I misunderstood what you are doing. If you do in fact need to pass the entire row of a data.frame into plyr with no grouping variable, perhaps you can treat it as an array with margin = 1? i.e adply(dat, 1, ...)

    Great introduction of plyr here: http://www.jstatsoft.org/v40/i01/paper

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