dt_log() starts a transcript: from that point on, every operation that
dtlog reports is appended to a text file, together with the call that
produced it. dt_log_end() closes the transcript. Start and end are up to
you; nothing is written before the first call or after the second.
Arguments
- file
Path of the text file. There is no default: name a path yourself, so that nothing is ever written to a place you did not choose.
NULLends the current transcript, sodt_log(NULL)is the same asdt_log_end().- append
Append to an existing file instead of overwriting it.
- code
Write the call above its log. Set to
FALSEfor the messages alone.- echo
Keep printing to the console as well.
FALSEwrites only to the file.
Details
Each operation is appended with a plain cat() that opens and closes the
file again, so the transcript stays readable while a long script is running
and survives a session that ends without dt_log_end() (only the closing
line is then missing).
Examples
path <- tempfile(fileext = ".txt")
dt_log(path, echo = FALSE)
dt <- data.table::as.data.table(mtcars)
dt[mpg > 20]
#> mpg cyl disp hp drat wt qsec vs am gear carb
#> <num> <num> <num> <num> <num> <num> <num> <num> <num> <num> <num>
#> 1: 21.0 6 160.0 110 3.90 2.620 16.46 0 1 4 4
#> 2: 21.0 6 160.0 110 3.90 2.875 17.02 0 1 4 4
#> 3: 22.8 4 108.0 93 3.85 2.320 18.61 1 1 4 1
#> 4: 21.4 6 258.0 110 3.08 3.215 19.44 1 0 3 1
#> 5: 24.4 4 146.7 62 3.69 3.190 20.00 1 0 4 2
#> 6: 22.8 4 140.8 95 3.92 3.150 22.90 1 0 4 2
#> 7: 32.4 4 78.7 66 4.08 2.200 19.47 1 1 4 1
#> 8: 30.4 4 75.7 52 4.93 1.615 18.52 1 1 4 2
#> 9: 33.9 4 71.1 65 4.22 1.835 19.90 1 1 4 1
#> 10: 21.5 4 120.1 97 3.70 2.465 20.01 1 0 3 1
#> 11: 27.3 4 79.0 66 4.08 1.935 18.90 1 1 4 1
#> 12: 26.0 4 120.3 91 4.43 2.140 16.70 0 1 5 2
#> 13: 30.4 4 95.1 113 3.77 1.513 16.90 1 1 5 2
#> 14: 21.4 4 121.0 109 4.11 2.780 18.60 1 1 4 2
dt[, kpl := mpg * 0.425]
#> mpg cyl disp hp drat wt qsec vs am gear carb kpl
#> <num> <num> <num> <num> <num> <num> <num> <num> <num> <num> <num> <num>
#> 1: 21.0 6 160.0 110 3.90 2.620 16.46 0 1 4 4 8.9250
#> 2: 21.0 6 160.0 110 3.90 2.875 17.02 0 1 4 4 8.9250
#> 3: 22.8 4 108.0 93 3.85 2.320 18.61 1 1 4 1 9.6900
#> 4: 21.4 6 258.0 110 3.08 3.215 19.44 1 0 3 1 9.0950
#> 5: 18.7 8 360.0 175 3.15 3.440 17.02 0 0 3 2 7.9475
#> 6: 18.1 6 225.0 105 2.76 3.460 20.22 1 0 3 1 7.6925
#> 7: 14.3 8 360.0 245 3.21 3.570 15.84 0 0 3 4 6.0775
#> 8: 24.4 4 146.7 62 3.69 3.190 20.00 1 0 4 2 10.3700
#> 9: 22.8 4 140.8 95 3.92 3.150 22.90 1 0 4 2 9.6900
#> 10: 19.2 6 167.6 123 3.92 3.440 18.30 1 0 4 4 8.1600
#> 11: 17.8 6 167.6 123 3.92 3.440 18.90 1 0 4 4 7.5650
#> 12: 16.4 8 275.8 180 3.07 4.070 17.40 0 0 3 3 6.9700
#> 13: 17.3 8 275.8 180 3.07 3.730 17.60 0 0 3 3 7.3525
#> 14: 15.2 8 275.8 180 3.07 3.780 18.00 0 0 3 3 6.4600
#> 15: 10.4 8 472.0 205 2.93 5.250 17.98 0 0 3 4 4.4200
#> 16: 10.4 8 460.0 215 3.00 5.424 17.82 0 0 3 4 4.4200
#> 17: 14.7 8 440.0 230 3.23 5.345 17.42 0 0 3 4 6.2475
#> 18: 32.4 4 78.7 66 4.08 2.200 19.47 1 1 4 1 13.7700
#> 19: 30.4 4 75.7 52 4.93 1.615 18.52 1 1 4 2 12.9200
#> 20: 33.9 4 71.1 65 4.22 1.835 19.90 1 1 4 1 14.4075
#> 21: 21.5 4 120.1 97 3.70 2.465 20.01 1 0 3 1 9.1375
#> 22: 15.5 8 318.0 150 2.76 3.520 16.87 0 0 3 2 6.5875
#> 23: 15.2 8 304.0 150 3.15 3.435 17.30 0 0 3 2 6.4600
#> 24: 13.3 8 350.0 245 3.73 3.840 15.41 0 0 3 4 5.6525
#> 25: 19.2 8 400.0 175 3.08 3.845 17.05 0 0 3 2 8.1600
#> 26: 27.3 4 79.0 66 4.08 1.935 18.90 1 1 4 1 11.6025
#> 27: 26.0 4 120.3 91 4.43 2.140 16.70 0 1 5 2 11.0500
#> 28: 30.4 4 95.1 113 3.77 1.513 16.90 1 1 5 2 12.9200
#> 29: 15.8 8 351.0 264 4.22 3.170 14.50 0 1 5 4 6.7150
#> 30: 19.7 6 145.0 175 3.62 2.770 15.50 0 1 5 6 8.3725
#> 31: 15.0 8 301.0 335 3.54 3.570 14.60 0 1 5 8 6.3750
#> 32: 21.4 4 121.0 109 4.11 2.780 18.60 1 1 4 2 9.0950
#> mpg cyl disp hp drat wt qsec vs am gear carb kpl
#> <num> <num> <num> <num> <num> <num> <num> <num> <num> <num> <num> <num>
dt_log_end()
#> dt_log: wrote 2 operations to '/tmp/RtmpaVzvdx/file191127b4f781.txt'
cat(readLines(path), sep = "\n")
#> # dtlog transcript, started 2026-09-05 22:15:29
#> # R version 4.6.1 (2026-06-24), data.table 1.18.6.1, dtlog 0.1.0
#> > dt[mpg > 20]
#> filter: removed 18 rows (56%), 14 rows remaining
#>
#> > dt[, `:=`(kpl, mpg * 0.425)]
#> mutate: new variable 'kpl' (double) with 25 unique values and 0% NA
#>
#> # dtlog transcript, ended 2026-09-05 22:15:29 (2 operations)