Question 1:

Who Variables Threshold Test % Correct
Alden job2 + height + diet3 + income2 0.5 84.1
Amanda income_level + job_new + body_type_buckets 0.5 70.7
Brenda income+height 0.5 83.2
James income + job + orientation + body_type 0.5 71.4
Albert height 0.5 83.0

Recall from Lec12.R and quiz

Question 2:

Important Principle of Coding: Don’t Repeat Yourself

# 1. Get gold & bitcoin data
# 2. Make column structure the same
# 3. Add variable type
gold <- Quandl("BUNDESBANK/BBK01_WT5511") %>% 
  select(Date, Value) %>% 
  mutate(type="Gold")

bitcoin <- Quandl("BAVERAGE/USD") %>% 
  rename(Value = `24h Average`) %>% 
  select(Date, Value) %>% 
  mutate(type="Bitcoin")

# Combine them into single data frame using bind_rows()
combined <- bind_rows(gold, bitcoin) %>% 
  # Group by here!
  group_by(type) %>% 
  # Then do the following ONLY ONCE:
  filter(year(Date) >= 2011) %>% 
  arrange(Date) %>% 
  mutate(
    Value_yest = lag(Value),
    rel_diff = 100 * (Value-Value_yest)/Value_yest
    )

# Plot
ggplot(combined, aes(x=Date, y=rel_diff, col=type)) +
  geom_line() +
  labs(y="% Change")

Question 3:

When parsing the time, what most of you did:

jukebox_hourly <- jukebox %>%
  mutate(
    date_time = parse_date_time(date_time, "%b %d %H%M%S %Y"),
    hour=hour(date_time)
    ) %>%
  group_by(hour) %>%
  summarise(count=n())

What’s wrong with this plot?

ggplot(data=jukebox_hourly, aes(x=hour, y=count)) + 
  geom_bar(stat="identity") +
  xlab("Hour of day") + 
  ylab("Number of songs played")

Need to change the time zone using date_time = with_tz(date_time, tz = "America/Los_Angeles"):

jukebox_hourly <- jukebox %>%
  mutate(
    date_time = parse_date_time(date_time, "%b %d %H%M%S %Y"),
    date_time = with_tz(date_time, tz = "America/Los_Angeles"),
    hour=hour(date_time)
    ) %>%
  group_by(hour) %>%
  summarise(count=n())
ggplot(data=jukebox_hourly, aes(x=hour, y=count)) + 
  geom_bar(stat="identity") +
  xlab("Hour of day") + 
  ylab("Number of songs played")

Your top 10 graveyard shift artists are not

artist n
OutKast 2533
Beatles, The 2219
Led Zeppelin 1617
Radiohead 1589
Rolling Stones, The 1522
Notorious B.I.G. 1382
Red Hot Chili Peppers, The 1318
Eminem 1311
Bob Dylan 1163
Talking Heads 1113

but are instead below. Not that different actually!

artist n
OutKast 1217
Beatles, The 765
Notorious B.I.G. 719
Led Zeppelin 644
Eminem 616
2Pac 568
Rolling Stones, The 529
Radiohead 490
Talking Heads 448
Tenacious D 435