10.57 ID Variables

20180723 From our observations so far we note that the variable (date) acts as an identifier as does the variable (location). Given a date and a location we have an observation of the remaining variables. Thus we note that these two variables are so-called identifiers. Identifiers would not usually be used as independent variables for building predictive analytics models.

# Note any identifiers.

id <- c("date", "location")

We might get a sense of how this works with the following which will list a random sample of locations and how long the observations for that location have been collected.

ds[id] %>%
  group_by(location) %>%
  count() %>%
  rename(days=n) %>%
  mutate(years=round(days/365)) %>%
  as.data.frame() %>%
  sample_n(10)

##        location days years
## 1      Richmond 5751    16
## 2      Watsonia 5751    16
## 3     Melbourne 5935    16
## 4   Tuggeranong 5781    16
## 5          Sale 5751    16
## 6  PerthAirport 5750    16
## 7   Williamtown 5751    16
## 8    Launceston 5782    16
## 9        Hobart 5935    16
## 10       Cairns 5782    16

The data for each location ranges in length from 4 years up to 9 years, though most have 8 years of data.

ds[id] %>%
  group_by(location) %>%
  count() %>%
  rename(days=n) %>%
  mutate(years=round(days/365)) %>%
  ungroup() %>%
  select(years) %>%
  summary()

##      years      
##  Min.   :11.00  
##  1st Qu.:16.00  
##  Median :16.00  
##  Mean   :15.55  
##  3rd Qu.:16.00  
##  Max.   :17.00

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