如何使用带有来自Postgres的时区的unix时间戳来格式化D3轴

Question

I'm trying to format my x-axis on a D3 line chart, but the values are completely wrong. The data originates from a Postgres database 'timestamp with timezone' column which I'm converting to json to serve up via D3.

D3 snippet

data.forEach(function(d) {
    d.timestamp = new Date(d.timestamp*1000);
    d.close=+d.close;
}
var timeFormat = d3.time.format("%d %b %y %X");
var x = d3.time.scale().range([ 0, width ]);
var xAxis = d3.svg.axis().scale(x).orient("bottom").tickFormat(timeFormat);
x.domain(d3.extent(data, function(d) {
        return d.timestamp;
    }));

Java conversion to JSON

ResultSet rs = st.executeQuery("select * from price_data order by timestamp);
...     
String.format("{\"timestamp\":\"%d\",\"close\":\"%f\"}",rs.getTimestamp("timestamp").getTime(),rs.getDouble("price"));

Result of axis formatting for timestamp with value 1426014732000

What I don't understand though is that the timeFormat function works fine when stepping through my javascript and calling it via a watch expression in Chrome...

Answer 1

Why this is happening I still don't know, but the fix was changing the data transformation to not multiply the timestamp by 1000 as suggested everywhere online.

data.forEach(function(d) {
  //d.timestamp = new Date(d.timestamp*1000);
  d.close=+d.close;
}
var timeFormat = d3.time.format("%d %b %y %X");
var x = d3.time.scale().range([ 0, width ]);
var xAxis = d3.svg.axis().scale(x).orient("bottom").tickFormat(timeFormat);
x.domain(d3.extent(data, function(d) {
        return d.timestamp;
    }));

Now the the timestamps are drawn correctly. Perhaps PostgreSql timestamps are already using milliseconds as expected in Javascript. I will investigate and report back for anyone who might be interested in this in future.

Answer 2

Looks as though you're doing most things right, but without the full code it's not really possible to tell. How are you computing the domain for the scale ? Something like:

x.domain(d3.extent(data));

Regardless, I've put together this simple example , which may help.