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Asked: 2026-06-16T01:46:54+00:00

I have database with time data. I want to interpolate the data to mach

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I have database with time data. I want to interpolate the data to mach e specific time step.

Id  Time                    humid   humtemp prtemp  press       t
1   2012-01-21 18:41:50     47.7    14.12   13.870  1005.70     -0.05277778
1   2012-01-21 18:46:43     44.5    15.37   15.100  1005.20     0.02861111
1   2012-01-21 18:51:35     43.2    15.88   15.576  1005.10     0.10972222
1   2012-01-21 18:56:28     42.5    16.17   15.833  1004.90     0.19111111
1   2012-01-21 19:01:21     42.2    16.31   15.986  1004.80     0.27250000
1   2012-01-21 19:06:14     41.8    16.47   16.118  1004.60     0.35388889
1   2012-01-21 19:11:07     41.6    16.51   16.177  1004.60     0.43527778

I want to obtain data with below time step doing interpolation. 

    Id                 Time       humid    humtemp prtemp  press        t   
    1   2012-01-21 18:45:00 ....    ...     .....   ....        ....
    1   2012-01-21 18:50:00 ....    
    1   2012-01-21 18:55:00 ....    
    1   2012-01-21 19:00:00 ....    
    1   2012-01-21 19:05:00 ....    
    1   2012-01-21 19:10:00 ....

I tried with diffrent method but I didn’t find the solution. For example I create zoo object.

   z <- zoo(MTS01m,order.by=MTS01m$Time)
   tstart2<-asP("2012-01-21 18:45:00")
   Ts<-1*60
   y <- merge(z, zoo(order.by=seq(tstart2, end(z), by=Ts)))
   xa <- na.approx(y)
   xs <- na.spline(y)

but error occur:

   Errore in approx(x[!na], y[!na], xout, ...) : 
   need at least two non-NA values to interpolate
   Inoltre: Warning message:
   In xy.coords(x, y) : si è prodotto un NA per coercizione

I create a secundary index t that start where I want to have data, but I don’t know how to use thid index.

Have you any suggestion?

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1 Answer

  1. Editorial Team

    Try this (assuming your time index is POSIXct):

    library(zoo)
st <- as.POSIXct("2012-01-21 18:45")
g <- seq(st, end(z), by = "15 min") # grid
na.approx(z, xout = g)

    See ?na.approx.zoo for more info.

    Note: Since the question did not provide the data in reproducible form we do so here:

    Lines <- "Id date Time humid humtemp prtemp press t1
1   2012-01-21 18:41:50     47.7    14.12   13.870  1005.70     -0.05277778
1   2012-01-21 18:46:43     44.5    15.37   15.100  1005.20     0.02861111
1   2012-01-21 18:51:35     43.2    15.88   15.576  1005.10     0.10972222
1   2012-01-21 18:56:28     42.5    16.17   15.833  1004.90     0.19111111
1   2012-01-21 19:01:21     42.2    16.31   15.986  1004.80     0.27250000
1   2012-01-21 19:06:14     41.8    16.47   16.118  1004.60     0.35388889
1   2012-01-21 19:11:07     41.6    16.51   16.177  1004.60     0.43527778"

library(zoo)
z <- read.zoo(text = Lines, header = TRUE, index = 2:3, tz = "")
st <- as.POSIXct("2012-01-21 18:45")
g <- seq(st, end(z), by = "15 min") # grid
na.approx(z, xout = g)

    giving:

                        Id    humid  humtemp   prtemp    press            t1
2012-01-21 18:45:00  1 45.62491 14.93058 14.66761 1005.376 -1.501706e-09
2012-01-21 19:00:00  1 42.28294 16.27130 15.94370 1004.828  2.500000e-01
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