Using loop to add columns in R

Question

My data set currently looks like this:

Contract number    FA      NAAR        q    
CM300             9746     47000    0.5010
UL350            80000       0      0.01234
RAD3421          50000     10000    0.9431

I would like to add a column with a randomly generated number (called trial) between 0-1 for each row, and compare this number to the value in column q with another column saying 'l' if q < trial, and 'd' if q > trial.

This is my code which accomplishes this task one time.

trial <- runif(3, min = 0, max = 1)
data2 <- mutate(data, trial)
data2 <- mutate(data, qresult = ifelse(data2$q <= data2$trial, 'l', 'd'))

My struggle is to get this to repeat for several trials , adding new columns onto the table with each repetition. I have tried several types of loops, and looked through several questions and cannot seem to figure it out. I am fairly new to R, so any help would be appreciated!

How many trials will you need to add? Are you looking to create a summary from all of the trials? Is adding all of those columns necessary, or are you just looking to perform a simulation? — bouncyball
– bouncyball, Commented Jun 2, 2017 at 15:19
Thank you for your feedback. I am trying to perform a simulation. I want to see which rows are marked 'd', and calculate the total FA and total NAAR fields for those rows. I am trying to run many trials in order to see how these values change. Is there a better way to do this? — Karly
– Karly, Commented Jun 2, 2017 at 17:08

akash87 · Accepted Answer · 2017-06-02 16:47:18Z

8

You may want to approach this using:

df <- data.frame(contract = c("CM300", "UL350", "RAD3421"), 
                 FA = c(9746, 80000, 50000), 
                 NAAR = c(47000, 0, 10000), 
                 q = c(0.5010, 0.01234, 0.9431))

trialmax <- 10
for(i in 1:trialmax){ 
  trial <- runif(3, min = 0, max = 1)
  df[ , paste0("trial", i)]   <- trial
  df[ , paste0("qresult", i)] <- ifelse(trial >= df$q, "l", "d")
  }

Here I assumed you want 10 trials, but you can change trialmax to whatever you want.

answered Jun 2, 2017 at 16:47

akash87

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Gregor Thomas · Accepted Answer · 2017-06-02 17:02:06Z

0

I'd keep things in a separate matrix for efficiency, only binding them on at the end. In fact, using vector recycling, this can be done very efficiently:

n_trials = 20
trials = matrix(runif(n_trials * nrow(data))], ncol = n_trials)
q_result = matrix(c("l", "d")[(trials > data$q) + 1], ncol = n_trials)
colNames(trials) = paste0("trial", seq_len(n_trials))
colNames(q_result) = paste0("qresult", seq_len(n_trials))
data = cbind(data, trials, q_result)

answered Jun 2, 2017 at 17:02

Gregor Thomas

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