I have a dataset that I am trying to manipulate in GraphLab. I want to convert a UNIX Epoch timestamp from the input file (converted to an SFrame) into a human readable format so I can do analysis based on hour of day and day of week.
time_array is the column/feature of the SFrame sf representing the timestamp, I have broken out just the EPOCH time to simplify things. I know how to convert the time of one row, but I want a vector operation. Here is what I have for one row.
time_array = sf['timestamp']
datetime.datetime.fromtimestamp(time_array[0]).strftime('%Y-%m-%d %H')
You can also get parts of the time from the timestamp to create another column, by which to filter (e.g., get the hour):
sf['hour'] = [x.strftime('%H')for x in sf['timestamp']]
So after staring at this for awhile and then posting the question it came to me, hopefully someone else can benefit as well. Use the .apply method with the datetime.datetime() function
sf['date_string'] = sf['timestamp'].apply(lambda x: datetime.datetime.fromtimestamp(x).strftime('%Y-%m-%d %H'))
you can also use the split_datetime API to split the timestamp to multiple columns:
split_datetime('timestamp',limit=['hour','minute'])
Related
I would like to store a time range (without dates) like "HH:MM-HH:MM".
Can you give me a hint, how can I implement it most easily? Maybe there is a way to use DateRangeField for this aim or something else.
Thanks for your spend time!
Time without date doesn't make much since if you ever need a range that span mid-night (days) You could always convert to text using to_char(<yourtimestamp>,'hh24.mi:ss') or extract the individual parts. Unfortunately Postgres does not provide an extract(time from <yourtimestamp>) function. The following function provides essentially that.
create or replace
function extract_tod(date_time_in timestamp without time zone)
returns time
language sql
as $$
select to_char(date_time_in, 'hh24:mi:ss')::time;
$$;
See here for timestatamp ranges and here for their associated functions. As for how to store then just store with the date
as a standard TIMESTAMP (date + time).
I'm trying to calculate difference of dates based on the current computer date, in ROS. Which function can I use to do that? Or atleast get the current date of computer.
Thanks in advance
You should try Google next time, but here:
ros::Time::now();
ros::Duration difference = ros::Time::now() - previous_time;
http://wiki.ros.org/roscpp/Overview/Time
EDIT:
To get a text string, you have to convert it: https://code.ros.org/trac/ros/ticket/2030
boost::posix_time thistime = from_time_t(difference);
Once you have it converted to boost::posix_time, you can:
std::string to_simple_string(thistime);
Which will spit it out like: "2002-Jan-01 10:00:01.123456789"
You can also see what thistime.date(); gives you, it looks like it might be simpler: http://www.boost.org/doc/libs/1_31_0/libs/date_time/doc/class_date.html
Mysql table one row =>
id = 1
time = "21:00" //datatype => TIME
name = "xyz"
while i am fetching the data
#person = #person.all
[#<persons id: 1, time: "2000-01-01 21:00:00, name: "xyz", created_at: "2014-03-19 05:13:43", updated_at: "2014-03-19 05:13:43", creator_id: nil">
#person[0].time # 2000-01-01 21:00:00
It should be "21:00" Right?
Why i am getting "2000-01-01 21:00:00" output any suggestion ??
After fetching data from query, you can format to time for displaying:
fetch all the records:
#person = #person.all
format to time.
#person.first.time.strftime("%H:%M")
for getting more information about date and time formating click here
#person[0].time returns the Ruby Time object for that value, which includes date. If you're outputting it directly to the console or browser window, Ruby is converting it to a default string representation of the Time object which, again, includes the date.
To format the time for display, you'll want to look at your options for date/time formatting using Rails' internationalization API.
try using strftime - it lets you specify format
ie something like:
#person[0].time.strftime("%m/%d/%Y %H:%M:%S")
Changing datatype from TIME TO VARCHAR :
It is not good approach. I think you should consider all the case about time, there is a lot possibility where you required TIME object to other operation like date.
If you store hours and minutes in VARCHAR then you can not perform any operation like TIME object. please think about, if you required hours or date from database in future but you have store only hours and minutes in database, you did not store (TIME Object)it, then it will be considered bad approach and failure.
you store TIME at the place of hours and minutes then It is good cause for future perspective.
If you store time object then you are store additional information with hours and minutes. If you will required Date, time, hours, minutes and even seconds then you can calculate by time formating.
If you store time then there is only one extra effort time formating that is negligible in perspective of performance.
To store TIME Object instead of hours and minutes in string format is always better.
I'm reading timestamp fields from a PostgreSQL database. The timestamp column is defined as:
my_timestamp TIMESTAMP WITH TIME ZONE DEFAULT NOW()
When reading from the database, I convert it to a boost timestamp like this:
boost::posix_time::ptime pt( boost::posix_time::time_from_string( str ) );
The problem seems to be that boost::posix_time::time_from_string() ignores the timezone.
For example:
database text string == "2013-05-30 00:27:04.8299-07" // note -07 timezone
boost::posix_time::to_iso_extended_string(pt) == "2013-05-30T00:27:04.829900"
When I do arithmetic with the resulting ptime object, the time is off by exactly 7 hours. Is there something better I should be doing to not lose the timezone information?
I think you should be using boost::local_date_time, which handles time zones. There is an example in the documentation that is very similar to what you're trying to do: http://www.boost.org/doc/libs/1_41_0/doc/html/date_time/examples.html#date_time.examples.seconds_since_epoch
EDIT: Boost supports date parsing with specific formats. http://www.boost.org/doc/libs/1_40_0/doc/html/date_time/date_time_io.html#date_time.format_flags
string inp("2013-05-30 00:27:04.8299-07");
string format("%Y-%m-%d %H:%M:%S%F%Q");
date d;
d = parser.parse_date(inp,
format,
svp);
// d == 2013-05-30 00:27:04.8299-07
I originally asked this question so many years ago, I don't even remember doing it. But since then, all my database date/time code on the client side has been greatly simplified. The trick is to tell PostgreSQL the local time zone when the DB connection is first established, and let the server automatically add or remove the necessary hours/minutes when it sends back timestamps. This way, timestamps are always in local time.
You do that with a 1-time call similar to this one:
SET SESSION TIME ZONE 'Europe/Berlin';
You can also use one of the many timezone abbreviations. For example, these two lines are equivalent:
SET SESSION TIME ZONE 'Asia/Hong_Kong';
SET SESSION TIME ZONE 'HKT';
The full list of timezones can be obtained with this:
SELECT * FROM pg_timezone_names ORDER BY name;
Note: there are over 1000 timezone names to pick from!
I have more details on PostgreSQL and timezones available on this post: https://www.ccoderun.ca/programming/2017-09-14_PostgreSQL_timestamps/index.html
I am trying to use df.iloc[] to locate a particular cell in dataframe. But we are unable to do it bcoz the cell contains date in timestamp format. I guess we need to convert that into int or string or float type. How do we do this?
that depends on the condition that that row is supposed to answer.
if you are looking for a specific range of dates try this :
dates=pd.date_range(A,Z)
day1DF= LWeekDF.ix[(LWeekDF['ReportTime']>=dates[A]) & (LWeekDF['ReportTime']<=dates[1])]
you now have a data frame with rows that answer to that condition.
this will work with other conditions as well.
if the dates are giving you problems try this
A=pd.datetime.date(a)