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Covariance by hand

In R, you can quickly compute various statistical measures using functions. The interviewer might be interested if you can replicate the calculations of these functions to ensure your understanding of what the functions do.

In this exercise, you will compute covariance by hand. The covariance measures the variability of two random variables.

Recall that the formula for the covariance of a sample is:

\( \sum_{i=1}^{n} \frac{(x_i - \overline{x})(y_i - \overline{y})}{n-1}\)

The df data frame is available in your environment with variables x and y.

本练习是课程的一部分

Practicing Statistics Interview Questions in R

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练习说明

  • Assign the number of observations in df to n.
  • Compute the covariance between x and y by hand.
  • Compute the covariance between x and y using a function from the stats package.

交互式实操练习

通过完成这段示例代码来试试这个练习。

# The number of observations
___ <- nrow(___)

# Compute covariance by hand
___((df$x-___(df$x))*(___-mean(df$y)))/(___-1)

# Compute covariance with function
___(df$x, ___)
编辑并运行代码