10.42 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   AliceSprings 4137    11
## 2    Witchcliffe 4105    11
## 3         Albany 4136    11
## 4        Walpole 4102    11
## 5     SalmonGums 4059    11
## 6         Albury 4137    11
## 7         Cairns 4137    11
## 8    Williamtown 4106    11
## 9  NorfolkIsland 4106    11
## 10  MountGambier 4136    11

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.   : 7.0  
##  1st Qu.:11.0  
##  Median :11.0  
##  Mean   :10.9  
##  3rd Qu.:11.0  
##  Max.   :12.0

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