In the StockDataAdapter.java file, there was a code block to avoid adding the same values that are already present in the stream:

for (StockUpdate stockUpdate : data) {
        if (stockUpdate.getStockSymbol()
            .equals(newStockUpdate.getStockSymbol())) {
        if (stockUpdate.getPrice()
            .equals(newStockUpdate.getPrice())
                    && stockUpdate.getTwitterStatus()
                    .equals(newStockUpdate.getTwitterStatus())) {
                return;
            }
            break;
        }
    }

However, it would be better to make the .add() method simpler by freeing it up from this responsibility of skipping duplicate values; now we can handle it in the flow. Let's start by extracting a method to check whether there is a duplicate value:

public void add(StockUpdate newStockUpdate) {
this.data.add(0, newStockUpdate);
    notifyItemInserted(0);
}

public boolean contains(StockUpdate newStockUpdate) {
    for (StockUpdate stockUpdate : data) {
        if (stockUpdate.getStockSymbol()
        .equals(newStockUpdate.getStockSymbol())) {
            if (stockUpdate.getPrice()
            .equals(newStockUpdate.getPrice())
                    && stockUpdate.getTwitterStatus()
                    .equals(newStockUpdate.getTwitterStatus())) {
                return true;
            }
            break;
        }
    }
    return false;
}

Now, the .contains() method can be used in the flow to add only new, non-existing entries:

.observeOn(AndroidSchedulers.mainThread())
.filter(update -> !stockDataAdapter.contains(update))
.subscribe(stockUpdate -> {
    Log.d("APP", "New update " + stockUpdate.getStockSymbol());
    noDataAvailableView.setVisibility(View.GONE);
    stockDataAdapter.add(stockUpdate);
    recyclerView.smoothScrollToPosition(0);
}, error -> {
    if (stockDataAdapter.getItemCount() == 0) {
        noDataAvailableView.setVisibility(View.VISIBLE);
    }
});

Note the following line:

.filter(update -> !stockDataAdapter.contains(update))

This means that no value that doesn't satisfy the condition will be let through.