R generates error when using the if statement and for loop

Question

The following is a data frame

   brand  production_cost  sell
   A      220               3
   B      180               1
   C      200               2
   D      240               4
   E      270               7
   F      200               4

If sell > 3 then investment = sell * production_cost

If sell < 3 then investment = sell * 0.5 * production_cost(50% of production cost)

I have tried by the following way:

   data <- read.table("Z:\\who.txt",header=TRUE)

   investment <- c(1,1,1,1,1,1)

  for(i in 1:6){
    if(data$sell[i]>3){
      investment[i] <- sell[i] * production_cost
    }else {
      investment[i] <- sell[i] * 0.5 * production_cost
    }
  } # end for loop

But the error is object sell not found

Then I have to compute

If investment >= 800 then produce = 1

If investment < 800 then produce = 0

Though I couldn't compute the variable investment I supposed it is as [by using calculator]

   investment <- c(330,90,200,960,1890,800)
   produce <- cut(investment,c(-Inf,800,Inf),labels=c("0","1"))

Here the problem is investment[6]=800. my attempt was to label it as 1. But it is labeling as 0.

Next i have to find the number of brands which are produce=1.

I tried this by the following way:

  sum=0

  for(i in 1:6){
    if(produce[i]==1)sum=sum+1
  } # end for loop

Is this right procedure and is there better way?

sell and production_cost do not exist but data$sell and data$production_cost do. post dput(data) so this is reproducible. look at ?ifelse — Jake Burkhead
– Jake Burkhead, Commented Jun 28, 2013 at 16:12
Tip: within(data, investment <- sell * production_cost * ifelse(sell>3, 1, 0.5)) — Ferdinand.kraft
– Ferdinand.kraft, Commented Jun 28, 2013 at 16:14
Given this and your previous question, you may want to start by reading cran.r-project.org/doc/manuals/R-intro.pdf, and start with Section 6.3 regarding dataframes. — Thomas
– Thomas, Commented Jun 28, 2013 at 16:16

Fernando · Accepted Answer · 2013-06-28 16:45:42Z

1

Use within, it creates an environment and returns a new dataframe:

newdata = within(data, {
investment = ifelse(sell > 3, sell * production_cost, sell * production_cost *0.5 )
})

newdata = within(newdata, {
    produce = ifelse(investment >= 800, 1, 0)
})

NOTE: this code sets

 investment = sell * production_cost * 0.5

if sell == 3

Hope it helps.

edited Jun 28, 2013 at 16:45

answered Jun 28, 2013 at 16:34

Fernando

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2 Comments

ABC Over a year ago

why doesn't here with work? and sometimes the expr argument of within works without braces and sometimes doesn't. Why?

Fernando Over a year ago

see ?with. Basically with returns the evaluated expression while within returns the modified dataframe.

Metrics · Accepted Answer · 2013-06-28 17:08:16Z

0

Assume your dataframe is sample. Following code is not tested

#You can use `ifelse` for first two problem

 sample$investment<-with(sample, ifelse(sell>3,sell * production_cost,sell * 0.5 * production_cost))
 sample$produce<-with(sample,ifelse(investment>=800,1,0))

#subset the sample with produce equal to 1 for part 3 and then use ddply from plyr to #count the number of brands

samplesub<-subset(sample, produce==1)

#number of brands 

install.packages("plyr")
library(plyr)
num_brand<-ddply(samplesub, .(brand), summarize, freq=length(brand))

#Alternative to `ddply` from plyr package
#Rather than using the `plyr` package, you can use the following simple code for part 3
num_brand<-with(samplesub,table(brand))

edited Jun 28, 2013 at 17:08

answered Jun 28, 2013 at 16:32

Metrics

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2 Comments

Fernando Over a year ago

plyr is too much overhead for this simple task. Use plyr to do complex stuff with your data.

Metrics Over a year ago

@Fernando : I will leave that to OP to decide.

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