Twitter added support for "@replies" beginning in May 2008,[3] with any combination of @ with a username being turned into a hyperlink to the profile. On March 30, 2009, Twitter updated the feature and renamed it "Mentions" (i.e., to "mention" user "@janedoe") so as to include non-reply posts directed at individual users.[4]
With pk=n_k/n being the fraction of the n_k samples from class k = {0,1} out of the total of n samples at node τ, the Gini impurity i(τ) is calculated as 1-p_0^2-p_1^2. The more discriminativ or clean a node is the lower is the value. A split will happen, if the decrease (delta_i) of the value is great for a given node. The gini decrease is the sum over all nodes in all trees of their delta_i's.
D. Liben-Nowell, and J. Kleinberg. Proceedings of the twelfth international conference on Information and knowledge management, page 556--559. New York, NY, USA, ACM, (2003)
D. Romero, B. Meeder, and J. Kleinberg. Proceedings of the 20th international conference on World wide web, page 695--704. New York, NY, USA, ACM, (2011)
T. Joachims. Proceedings of the eighth ACM SIGKDD international conference on Knowledge discovery and data mining, page 133--142. New York, NY, USA, ACM, (2002)
J. Yang, and J. Leskovec. Proceedings of the 2010 IEEE International Conference on Data Mining, page 599--608. Washington, DC, USA, IEEE Computer Society, (2010)
J. Chen, R. Nairn, L. Nelson, M. Bernstein, and E. Chi. Proceedings of the SIGCHI Conference on Human Factors in Computing Systems, page 1185--1194. New York, NY, USA, ACM, (2010)
R. Jäschke, L. Marinho, A. Hotho, L. Schmidt-Thieme, and G. Stumme. Knowledge Discovery in Databases: PKDD 2007, 11th European Conference on Principles and Practice of Knowledge Discovery in Databases, Warsaw, Poland, September 17-21, 2007. Proceedings, volume 4702 2007 of Lecture Notes in Computer Science, page 506--514. Berlin, Heidelberg, Springer, (2007)
Z. Ma, A. Sun, and G. Cong. Proceedings of the 35th international ACM SIGIR conference on Research and development in information retrieval, page 1173--1174. New York, NY, USA, ACM, (2012)
J. Leskovec, D. Huttenlocher, and J. Kleinberg. Proceedings of the 19th international conference on World wide web, page 641--650. New York, NY, USA, ACM, (2010)