Quiz 1 - Addendum

Classwork 7

Descriptive Statistics

The following provides the percentage of the correct answers for each question in Quiz 1 - Addendum:

Question 1. data.frame

In a data frame, what form does a variable take?

Answer: Column

• This slide in Lecture 7 explains what makes a data.frame tidy. In our course, all given data.frames are tidy.
  • It’s been a while since we discussed variable-column, observation-row, and value-cell terminologies in a tidy data.frame, but these concepts are crucial for conducting data analysis.
• In a data.frame:
  • A variable takes a column
  • An observation takes a row
  • A value takes a cell

Question 2. left_join()

df_joined <- df_1 |> ___(df_2)

• Fill in the blank (___) to join the two related data.frames, df_1 and df_2, in a way that keeps all observations and variables in the data.frame df_1.

Answer: left_join

df_joined <- df_1 |> left_join(df_2)

• This slide in Lecture 14 and this slide in Lecture 12 explain join and left_join().

Question 3. == (Equality operator)

df_filtered <- df |> filter(num __ 9) 

• Fill in the blank (___) to keep observations, in which the value of the num variable is equal to 9.

Answer: ==

df_filtered <- df |> filter(num == 9) 

• This slide and many examples from class R scripts explain this equality operator.

Question 4. != (Not-equal operator)

non_dec <- df |> filter(month ___ 12)

• Fill in the blank (___) to keep observations, in which the value of the month is not equal to 12 in the data.frame df

Answer: !=

non_dec <- df |> filter(month != 12)

• This slide and Line 63-64 in this class R script in Lecture 14 explain a not-equal operator, != (not equal to).

Question 5. | (Or operator)

df_filtered <- df |> filter(subject == "DANL" ___ subject == "ECON")

• Fill in the blank (___) to keep observations, in which the value of the subject variable is either “DANL” or “ECON”

Answer: |

df_filtered <- df |> filter(subject == "DANL" | subject == "ECON")

• This slide and this slide in Lecture 14 explain logical operation, | (or).

• Please note that | is not the letter “I” or “l,” but a vertical bar character.

• On a keyboard, | is located above the Enter/Return key.

Discussion

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