R h2o gsub null pointer - regex

Question

I'm using the h2o package in R and trying to do some data manipulation but having some issues with the sub/gsub functions.
Here's my code:
library(h2o)
# Start cluster
localH2O = h2o.init(nthreads = 2)
# Create data set
dat1.mini <- structure(list(id = c("7927751403363142656", "18236986451472797696",
"5654946373641778176", "14195690822403907584", "1693303484298446848",
"1.1362181921561e+19", "11694645532962195456", "1221431312630614784",
"1987127670789791488", "379819848497418688"), click = c("0",
"0", "0", "0", "0", "0", "0", "1", "0", "0"), hour = c("14102118",
"14102217", "14102812", "14102912", "14102820", "14102401", "14102117",
"14102312", "14102301", "14102414"), C1 = c("1005", "1005", "1005",
"1002", "1005", "1005", "1005", "1005", "1005", "1005"), banner_pos = c("1",
"1", "0", "0", "0", "0", "1", "1", "0", "0"), site_id = c("b7e9786d",
"e151e245", "85f751fd", "ee4c822c", "85f751fd", "85f751fd", "e5c60a05",
"e151e245", "1fbe01fe", "1fbe01fe"), site_domain = c("b12b9f85",
"7e091613", "c4e18dd6", "c4e18dd6", "c4e18dd6", "c4e18dd6", "7256c623",
"7e091613", "f3845767", "f3845767"), site_category = c("f028772b",
"f028772b", "50e219e0", "50e219e0", "50e219e0", "50e219e0", "f028772b",
"f028772b", "28905ebd", "28905ebd"), app_id = c("ecad2386", "ecad2386",
"685d1c4c", "ecad2386", "92f5800b", "f02cb7ab", "ecad2386", "ecad2386",
"ecad2386", "ecad2386"), app_domain = c("7801e8d9", "7801e8d9",
"2347f47a", "7801e8d9", "ae637522", "2347f47a", "7801e8d9", "7801e8d9",
"7801e8d9", "7801e8d9"), app_category = c("07d7df22", "07d7df22",
"8ded1f7a", "07d7df22", "0f2161f8", "f95efa07", "07d7df22", "07d7df22",
"07d7df22", "07d7df22"), device_id = c("a99f214a", "a99f214a",
"a99f214a", "8374cacf", "a99f214a", "8a5908a5", "a99f214a", "a99f214a",
"a99f214a", "a99f214a"), device_ip = c("3214d61e", "d5623936",
"419e166e", "698846d6", "c2d9c2f2", "40817190", "edd10fc1", "e4c6e857",
"05d3adbe", "6929d972"), device_model = c("a0f5f879", "69f9dd0e",
"46a414f4", "12edfe21", "4ffd3a7e", "04f5b394", "779d90c2", "1f0bc64f",
"293291c1", "d787e91b"), device_type = c("1", "1", "1", "0",
"1", "1", "1", "1", "1", "1"), device_conn_type = c("0", "0",
"3", "0", "3", "0", "0", "0", "0", "0"), C14 = c("16208", "20277",
"23224", "17566", "21189", "20633", "19771", "17264", "15703",
"20108"), C15 = c("320", "320", "320", "320", "320", "320", "320",
"320", "320", "320"), C16 = c("50", "50", "50", "50", "50", "50",
"50", "50", "50", "50"), C17 = c("1800", "2281", "2676", "479",
"2424", "2374", "2227", "1872", "1722", "2299"), C18 = c("3",
"3", "0", "3", "1", "3", "0", "3", "0", "2"), C19 = c("167",
"47", "35", "39", "161", "39", "679", "39", "35", "1327"), C20 = c("100077",
"100181", "100176", "100074", "100189", "-1", "100074", "-1",
"-1", "-1"), C21 = c("23", "42", "221", "23", "71", "23", "48",
"23", "79", "52")), .Names = c("id", "click", "hour", "C1", "banner_pos",
"site_id", "site_domain", "site_category", "app_id", "app_domain",
"app_category", "device_id", "device_ip", "device_model", "device_type",
"device_conn_type", "C14", "C15", "C16", "C17", "C18", "C19",
"C20", "C21"), row.names = c(NA, 10L), class = "data.frame")
# Load data to cluster
dat.mini.hex <- as.h2o(localH2O, dat1.mini)
# Attempt to grab substring of first 6 characters from hour column
dat.mini.hex$hr <- h2o.sub('^(.{6}).*$','\\1', dat.mini.hex$hour)
dat.mini.hex$hr <- h2o.gsub('(.+)..','\\1', dat.mini.hex$hour)
All of these attempts result in the following error:
Error in .h2o.__remoteSend(client, .h2o.__PAGE_EXEC2, str = expr) :
http://127.0.0.1:54321/2/Exec2.json returned the following error:
class java.lang.NullPointerException

Answer 1

The error occurs because hour is a numeric column. The function h2o.sub and h2o.gsub do not work with numeric data.
The command str(dat.mini.hex$hour) will show you that hour is a numeric column.
str(dat.mini.hex$hour)
You can convert hour to a factor and save the result in a new column hour2.
dat.mini.hex$hour2 <- as.factor(dat.mini.hex$hour)
Now, you can use h2o.sub. However, I suppose you will not like the result...
h2o.sub('^(.{6}).*$','\\1', dat.mini.hex$hour2)
# hour2
# 1 \\1
# 2 \\1
# 3 \\1
# 4 \\1
# 5 \\1
# 6 \\1
As you can see, h2o.sub uses \\1 literally but not for the first matching group. This behaviour is in contrast to base R's sub.
You can change your regex and replace the characters after the first six ones with the empty string.
h2o.sub('(?<=^.{6}).*$','', dat.mini.hex$hour2)
# hour2
# 1 141021
# 2 141022
# 3 141028
# 4 141029
# 5 141028
# 6 141024
Here, (?<=^.{6}) is a positive lookbehind. It matches the position that is preceded by the beginning of the string and the first 6 digits.