Linegraphs

Linegraphs are typically used when looking at time series data, that is, when we have information on how a variable changes over time. Hence, there is a natural ordering to the data when observing how something changes over time, and therefore, linegraphs should be avoided if there is no sequential ordering of a variable. Let's again look at the hourly temperature data, but this time only for Newark International Airport in January. This can be done by first subsetting the data as follows:

Newark.Jan <- weather[weather$origin == "EWR" & weather$month == 1, ]


Task: Get a feel for what is contained in the new data set for hourly temperatures at Newark International Airport in January using functions mentioned earlier.

Try using the head and dim functions.

head(Newark.Jan)
## # A tibble: 6 × 15
##   origin  year month   day  hour  temp  dewp humid wind_dir wind_speed wind_gust
##   <chr>  <int> <int> <int> <int> <dbl> <dbl> <dbl>    <dbl>      <dbl>     <dbl>
## 1 EWR     2013     1     1     1  39.0  26.1  59.4      270      10.4         NA
## 2 EWR     2013     1     1     2  39.0  27.0  61.6      250       8.06        NA
## 3 EWR     2013     1     1     3  39.0  28.0  64.4      240      11.5         NA
## 4 EWR     2013     1     1     4  39.9  28.0  62.2      250      12.7         NA
## 5 EWR     2013     1     1     5  39.0  28.0  64.4      260      12.7         NA
## 6 EWR     2013     1     1     6  37.9  28.0  67.2      240      11.5         NA
## # ℹ 4 more variables: precip <dbl>, pressure <dbl>, visib <dbl>,
## #   time_hour <dttm>
dim(Newark.Jan)
## [1] 742  15


To produce linegraphs using ggplot we use the geom_line function. Hence, our linegraph for the hourly temperatures at Newark International Airport in January 2013 can be created as follows:

ggplot(data = Newark.Jan, mapping = aes(x = time_hour, y = temp)) +
  geom_line() +
    labs(x = "Time (Hours)", y = "Temperature",
        title = "Hourly Temperature at Newark Airport in January 2013")
Figure 18: Hourly temperature at Newark Airport in January 2013.

Figure 16: Figure 18: Hourly temperature at Newark Airport in January 2013.

Before moving on to the next section, consider the following:

  • In the code for the linegraph above, why has time_hour been plotted on the x-axis and not hour?
  • Why should linegraphs be avoided when there is no sequential ordering of the data?
  • Why are linegraphs used when time is the explanatory variable?
  • Describe the trend in hourly temperature at Newark International Airport in January 2013.