spark1.5引进内置函数

在Spark 1.5.x版本，增加了一系列内置函数到DataFrame API中，并且实现了code-generation的优化。与普通的函数不同，DataFrame的函数并不会执行后立即返回一个结果值，而是返回一个Column对象，用于在并行作业中进行求值。Column可以用在DataFrame的操作之中，比如select，filter，groupBy等。函数的输入值，也可以是Column。

聚合函数:

approxCountDistinct, avg, count, countDistinct, first, last, max, mean, min, sum, sumDistinct

集合函数:

array_contains, explode, size, sort_array

日期/时间函数：

日期时间转换
unix_timestamp, from_unixtime, to_date, quarter, day, dayofyear, weekofyear, from_utc_timestamp, to_utc_timestamp
从日期时间中提取字段
year, month, dayofmonth, hour, minute, second

日期/时间函数：

日期/时间计算
datediff, date_add, date_sub, add_months, last_day, next_day, months_between
获取当前时间等
current_date, current_timestamp, trunc, date_format

数学函数：

abs, acros, asin, atan, atan2, bin, cbrt, ceil, conv, cos, sosh, exp, expm1, factorial, floor, hex, hypot, log, log10, log1p, log2, pmod, pow, rint, round, shiftLeft, shiftRight, shiftRightUnsigned, signum, sin, sinh, sqrt, tan, tanh, toDegrees, toRadians, unhex

混合函数:

array, bitwiseNOT, callUDF, coalesce, crc32, greatest, if, inputFileName, isNaN, isnotnull, isnull, least, lit, md5, monotonicallyIncreasingId, nanvl, negate, not, rand, randn, sha, sha1, sparkPartitionId, struct, when

字符串函数:

ascii, base64, concat, concat_ws, decode, encode, format_number, format_string, get_json_object, initcap, instr, length, levenshtein, locate, lower, lpad, ltrim, printf, regexp_extract, regexp_replace, repeat, reverse, rpad, rtrim, soundex, space, split, substring, substring_index, translate, trim, unb

窗口函数:

cumeDist, denseRank, lag, lead, ntile, percentRank, rank, rowNumber

ase64, upper