For loop and add a new column to dataframe in R

I have a dataset called tweet_new, and tweet content is in "text" column in this dataset.

I will perform a sentiment analysis on each tweet content using get_avg_sentiment function below:

get_avg_sentiment = function(tweet){sentiment = sentiment_by(tweet)}

I want to use a for loop to run the function on all tweets in database, and then add a new column to store the result sentiment result. How can I do that? Thanks!