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R for Data Analytics MCQ - Data Import and Data Cleaning

11 Which function removes observations containing missing values?

na.omit() returns an object with incomplete observations removed.

12 Which expression returns only complete rows from a data frame df?

complete.cases() returns TRUE for rows that contain no missing values.

13 What does unique(x) return?

unique() removes duplicate occurrences and returns the distinct values.

14 Which function identifies duplicated elements?

duplicated() returns a logical vector indicating duplicated elements.

15 What does which(is.na(x)) return?

which() converts TRUE positions from is.na(x) into their numeric indices.

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Question:

Which argument of read.csv() can be used to specify strings that should be interpreted as missing values?

A. missing
B. null.value
C. na.strings
D. na.value

Correct answer: C

Explanation:

The na.strings argument specifies character values that should be converted to NA.

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