Accessing and Modifying Key Columns

Setup

Starting with our df_mini, let’s rename columns to truly custom names.

library(trackframe)

df <- trackframe::df_mini

df

##                  time      northing       easting      id
## 1 2025-10-14 13:48:46  0.000000e+00  0.0000000000 track_1
## 2 2025-10-14 13:49:46 -6.375425e-05 -0.0009523287 track_1
## 3 2025-10-14 13:50:46 -3.326043e-04 -0.0012222081 track_1
## 4 2025-10-14 13:51:46 -6.402753e-04 -0.0020070494 track_1
## 5 2025-10-14 13:52:46 -2.096415e-04 -0.0029277994 track_1

colnames(df) <- c('when', 'up', 'right', 'who')

Now let’s convert this dataframe to a trackframe object, telling as.trackframe which columns are the key columns.

tf <- as.trackframe(
  df,
  time_col = 'when',
  easting_col = 'right',
  northing_col = 'up',
  id_col = 'who',
  crs = NA
)
tf

##                  when            up         right     who
## 1 2025-10-14 13:48:46  0.000000e+00  0.0000000000 track_1
## 2 2025-10-14 13:49:46 -6.375425e-05 -0.0009523287 track_1
## 3 2025-10-14 13:50:46 -3.326043e-04 -0.0012222081 track_1
## 4 2025-10-14 13:51:46 -6.402753e-04 -0.0020070494 track_1
## 5 2025-10-14 13:52:46 -2.096415e-04 -0.0029277994 track_1

Accessing key contents

Without changing our funky column names, we can access the key columns in a generic way:

easting(tf)

## [1]  0.0000000000 -0.0009523287 -0.0012222081 -0.0020070494 -0.0029277994

northing(tf)

## [1]  0.000000e+00 -6.375425e-05 -3.326043e-04 -6.402753e-04 -2.096415e-04

time(tf)

## [1] "2025-10-14 13:48:46 UTC" "2025-10-14 13:49:46 UTC"
## [3] "2025-10-14 13:50:46 UTC" "2025-10-14 13:51:46 UTC"
## [5] "2025-10-14 13:52:46 UTC"

id(tf)

## [1] "track_1" "track_1" "track_1" "track_1" "track_1"

Modifying key columns

We can also update the contents of columns using these same functions:

time(tf) <- time(tf) + as.difftime(1, unit = 'days')
tf$when # sucessfully updated

## [1] "2025-10-15 13:48:46 UTC" "2025-10-15 13:49:46 UTC"
## [3] "2025-10-15 13:50:46 UTC" "2025-10-15 13:51:46 UTC"
## [5] "2025-10-15 13:52:46 UTC"

Accessing key column names

If we need to access the column names, we can do that with the *_col functions.

time_col(tf)

## [1] "when"

easting_col(tf)

## [1] "right"

northing_col(tf)

## [1] "up"

id_col(tf)

## [1] "who"

Alternatively, we can use the tf_colnames function. Note: this will just return the names of key columns, not any other columns in the trackframe. The vector returned by tf_colnames also itself has names indicating which key column is which.

tf$why <- "just because"

colnames(tf)

## [1] "when"  "up"    "right" "who"   "why"

tf_colnames(tf)

##     time northing  easting       id 
##   "when"     "up"  "right"    "who"

Modifying key column names

tf_colnames() and the individual *_col() functions can be used to change the column names as well.

id_col(tf) <- "track_id"

tf_colnames(tf) # updated

##       time   northing    easting         id 
##     "when"       "up"    "right" "track_id"

tf_colnames(tf)[["time"]] <- "timestamp"
tf_colnames(tf) # updated

##        time    northing     easting          id 
## "timestamp"        "up"     "right"  "track_id"

Changing which are key columns

What if you want to change which column within the data frame is identified as a key column. That can be done by rerunning as.trackframe with a new column name. For example:

# create new columns that we want to be the new coordinates
tf$up_10x <- 10 * tf$up
tf$right_10x <- 10 * tf$right

# up/right and up_10x/right_10x are both part of the trackframe
colnames(tf)

## [1] "timestamp" "up"        "right"     "track_id"  "why"       "up_10x"   
## [7] "right_10x"

# still same as original
min(easting(tf))

## [1] -0.002927799

min(northing(tf))

## [1] -0.0006402753

tf_colnames(tf) # also unchanged

##        time    northing     easting          id 
## "timestamp"        "up"     "right"  "track_id"

# update which columns are used as key columns

tf <- as.trackframe(tf, easting = "right_10x", northing = "up_10x", crs = NA)

# Now the easting and northing values are coming from the *_10x columns
min(easting(tf))

## [1] -0.02927799

min(northing(tf))

## [1] -0.006402753

# likewise, tf_colnames is updated
tf_colnames(tf)

##        time          id    northing     easting 
## "timestamp"  "track_id"    "up_10x" "right_10x"

# up and right (1x) columns are still there.
# They are just not identified as the easting and northing columns
colnames(tf)

## [1] "timestamp" "up"        "right"     "track_id"  "why"       "up_10x"   
## [7] "right_10x"

Accessing and updating crs

crs() can be used to access and update crs. crs_type() can

crs(tf)

## [1] NA

crs_type(tf)

## [1] "nongeoreferenced"

crs(tf) <- "EPSG:32632"
crs(tf)

## [1] "EPSG:32632"

crs_type(tf)

## [1] "projected"

Accessing and Modifying Key Columns

Brock

2025-11-17