# Functional Review

Question:
I’m having trouble with functionals in general. I have my sample sizes and I just want to be able to be able to find the mean for each sample size (need to get sample_sizes vector into the ? position).

If someone could take the time to explain how it (or functionals in general) works I would really appreciate it.

My Code:

``````set.seed(4)
sample_sizes <- seq(from = 5, to = 2876, by = 29)
map_dbl(sample_sizes, mean(sample(houses\$SalePrice, size = ?)))
``````
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The mean of the whole sample is: `parameter <- mean(houses\$SalePrice)`

We create different sample sizes with `sample_sizes <- seq(from = 5, to = 2876, by = 29)`

We want to calculate the difference between the parameter and the mean of all the samples. We use the `map_dbl` to do so at once, instead of repeating the calculations one after the other.

In the code below, we pick a particular sample_sizes, say `5`. We use the python lambda function style to create a function we only need for this operation `function(x)`.

So this function takes `5` as `x`, supplies it to the `sample()` and takes a sample size of `5` for this run. The `mean()` is then used to average the result of the five samples of `houses\$SalePrice` and this is subtracted from `parameter` .

`sampling_errors <- map_dbl(sample_sizes, function(x) parameter - mean(sample(houses\$SalePrice, size = x)))`

See code below.

``````parameter <- mean(houses\$SalePrice)

sample_sizes <- seq(from = 5, to = 2876, by = 29)

sampling_errors <- map_dbl(sample_sizes, function(x) parameter - mean(sample(houses\$SalePrice, size = x))
)
``````
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Ah so you made a custom function with size as the input. Makes sense thank you

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