# tidyr::hoist()
x %>%
  filter(activityType == 'ECOMMERCE') %>%
  select(id, sessionId, activityTime, activityType, ecommerce, customDimension) %>%
  hoist(ecommerce,
        action_type = c('actionType'),
        transaction_id = c('transaction', 'transactionId'),
        transaction_revenue = c('transaction', 'transactionRevenue'),
        products = 'products',
        ecommerce_type = 'ecommerceType') %>%
  unnest_longer(products) %>% unnest_wider(products) %>%
  filter(!is.na(transaction_id)) %>%
  select(-ecommerce, -customDimension)

# map inside mutate
x %>%
  filter(activityType == "ECOMMERCE") %>%
  select(id, sessionId, activityTime, ecommerce) %>%
  mutate(transaction = map(ecommerce, "transaction"),
         transactionRevenue = map_dbl(transaction, ~.[["transactionRevenue"]] %||% NA),
         transactionId = map_chr(transaction, ~.[["transactionId"]] %||% NA)) %>%
  filter(!is.na(transactionRevenue)) %>%
  mutate(actionType = map_chr(ecommerce, ~.[['actionType']] %||% NA),
         products = map(ecommerce, 'products')) %>%
         unnest(products) %>%
  mutate(productSku = map_chr(products, ~.[['productSku']]),
         productName = map_chr(products, ~.[['productName']]),
         itemRevenue = map_chr(products, ~.[['itemRevenue']]) %>% as.numeric(),
         productQuantity = map_chr(products, ~.[['productQuantity']]) %>% as.numeric()) %>%
  select(-transaction, -ecommerce, -products)