1. Probability theory & random processes (continuous/discrete distributions, markov chains, MCMC algorithms)
2. Mathematical knowledge of different kinds of parametric/non-parametric statistical inference techniques Linear Algebra
3. Understanding of data structures & the ability to carry out asymptotic analysis of algorithms
4. Knowledge of various kinds of algorithms in the field of Information Retrieval
5. Programming/implementation skills & expert level understanding of any one high-level object oriented programming language & one scripting language.
6. UNIX (scripting) skills & the ability to use UNIX tools such as sed, awk, grep, join, comm, diff etc
7. Knowledge of various tools in Hadoop & the ability to write SQL-like queries.