How to Multiple functions to a data frame

Question

I am creating a headcount model for a contact center. I would like to apply erlang c to a new column of my forecasted data (forecast pulled in via RODBC con)

When I apply my erlang c formula, I get multiple warnings, mostly repeating themselves. The formula does run, but only the 1st line is accurate.

Warning messages:

1: In 1:agents : numerical expression has 96 elements: only the first used

2: In while (gos < gos_target * (gos_target > 1)/100) { : the condition has length > 1 and only the first element will be used

3: In 1:agents : numerical expression has 96 elements: only the first used

4: In while (gos < gos_target * (gos_target > 1)/100) { : the condition has length > 1 and only the first element will be used

The problem is that I need some of the input for the function to pull from the data frame

I need the function to take the call volume and AHT from that current row in the data frame and work out a headcount requirement

The data is a basic table that consist of date, day, month AHT & Calls Columns

I have tried different methods of applying it:

I have used Lapply
I have tried adding it by creating new column
I have tried using rep function
I have tried using for loop

#

  Interval <- 15
  Calls <- Should pull from Data
  Duration <- Should pull from Data
  Wait_time <- 20
  gos_target <- 90
  Shrinkage <- 21
  Rate <- Calls *(60/Interval)

  intensity <- function(rate, duration, interval = 60) {
    (rate / (60 * interval)) * duration
  }

  erlang_c <- function(agents, rate, duration, interval = 60) {
    int <- intensity(rate, duration, interval)
    erlang_b_inv <- 1
    for (i in 1:agents) {
      erlang_b_inv <- 1 + erlang_b_inv * i / int
    }
    erlang_b <- 1 / erlang_b_inv
    agents * erlang_b / (agents - int * (1 - erlang_b))
  }

  service_level <- function(agents, rate, duration, target, interval = 60) {
    pw <- erlang_c(agents, rate, duration, interval)
    int <- intensity(rate, duration, interval)
    1 - (pw * exp(-(agents - int) * (target / duration)))
  }

  resource <- function(rate, duration, target, gos_target, interval = 60) {
    agents <-round(intensity(rate, duration, interval) + 1)
    gos <- service_level(agents, rate, duration, target, interval)
    while (gos < gos_target * (gos_target > 1) / 100) {
      agents <- agents + 1
      gos <- service_level(agents, rate, duration, target, interval)
    }
    return(c(ceiling(agents/(1-(Shrinkage/100)))))
  }

  resource(Calls, Duration, Wait_time, gos_target, 15)

#

I need each column to give me the accurate headcount required. when i run it for one, line of data, any line, the answer is always accurate. as soon as i have more than one row of data i my headcount results calculates, however is always inaccurate, by 5 to 15 agents

Welcome to SO. Could you please try to reduce your problem to a lighter problem. So it would be easier for us to understand and you might find your solution on the way. But, the warning seems pretty explicit: gos is more than one dimensional. It shouldn't be the case. You should try to see where / why you have length(gos)>1 — Emmanuel-Lin
– Emmanuel-Lin, Commented Feb 5, 2019 at 13:55
That code isn't erlang, so why does your question have an erlang tag? — 7stud
– 7stud, Commented Feb 5, 2019 at 20:17

Bob Zimmermann · Accepted Answer · 2019-02-05 14:45:56Z

1

If I understand correctly, the Calls and Duration arguments are potentially vectors, whereas the other arguments are parameters to the model. One simple solution would be to vectorize the function itself:

vresource <- Vectorize(resource)

Vectorize does the work of converting a function to one which accepts both vectors and constant v values and applying across those which are vectors in parallel. This would produced the following result with the following data frame:

R> df <- data.frame(Calls=c(1,5,3,7), Duration=c(30,50,45,10))
R> with(df, vresource(Calls, Duration, Wait_time, gos_target, 15))
[1] 2 3 3 2

This could then be easily added to the data frame by assigning it to a new column, e.g., df$resource <- with(df, vresource(Calls, Duration, Wait_time, gos_target, 15)).

answered Feb 5, 2019 at 14:45

Bob Zimmermann

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1 Comment

Wayne Van tonder Over a year ago

It Worked, Thanks so much

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