 # A/B Testing for ShoeFly.com - Step 4

I continue to get this error when I execute my code, any assistance would be greatly appreciated

``````# define clicks_by_utm here:
percentage_by_utm <- clicks_by_utm %>%
group_by(utm_source) %>%
mutate(percentage = count/sum(count))
``````
``````Error in sum(count): invalid 'type' (closure) of argument
``````

Hide

``````percentage_by_utm
``````
``````Error in eval(expr, envir, enclos): object 'percentage_by_utm' not found
``````

I tried to solve for this by adding: summarize(count = n() ) %>%
above the mutate line
but that set each of the percentages to 25% rather than the % for click rate by UTM_Source

Here is the instructions for step 4

To find the percentage of people who clicked on ads from each `utm_source` , we need to add a new column to `ad_clicks` that stores the `count` of clicks (or the `count` of not clicking) divided by the total number of ad views.

Group `clicks_by_utm` by `utm_source` and pipe the result into `mutate()` , creating a new column `percentage` that is defined as `count/sum(count)` .

Save your result to `percentage_by_utm` and view it. Open the hint for a description of the `percentage_by_utm` data frame.

Hint

To group together the rows of `clicks_by_utm` with the same value for `utm_source` with `group_by()` :

percentage_by_utm <- clicks_by_utm %>% group_by(utm_source) %>%

To add a column that stores the percentage of users who did or did not click on the ad, pipe the result from the grouping into `mutate()` and create a new column `percentage` defined as `count/sum(count)` :

percentage_by_utm <- clicks_by_utm %>% group_by(utm_source) %>% mutate(percentage = count/sum(count))

• `count` represents the number of users who did or did not click on an ad
• `sum(count)` represents the total number of users who saw the ad

`percentage_by_utm` will now contain the click and non-click rates for each `utm_source` / `ad_clicked` grouping.