tolong: Create a long file from a wide file

In gmonette/spida2: Collection of tools developed for the Summer Programme in Data Analysis 2000-2012

Create a long file from a wide file

Description

Uses a minimal number of arguments to create a long file using stats::reshape. Produces output even when long variable names and time values are not fully crossed.

Usage

tolong(
  data,
  sep = "_",
  timevar = "time",
  idvar = "id",
  ids = 1:nrow(data),
  expand = TRUE,
  safe_sep = "#%@!",
  reverse = F,
  ...
)

long(
  data,
  sep = "_",
  timevar = "time",
  idvar = "id",
  ids = 1:nrow(data),
  expand = TRUE,
  safe_sep = "#%@!",
  reverse = F,
  ...
)

Arguments

data	wide data frame
sep	(default '_') single character separator between long names and 'time' value. Variable names with this separator are transformed to long variables.
timevar	(default 'time') names of variable in output long file to identify occasions. Its values are taken from the suffix following the 'sep' character in each time-varying variable.
idvar	(default: 'id') the variable name used in the output long file to identify rows in the input wide file. It may exist in the input wide file and must, in that case, have a unique value in each row. If it does not exist, it will be created with values equal to the row numbers of the input wide file.
ids	(default 1:nrow(data)) values for idvar in long file if the variable idvar does not exist in in the input wide file. Ignored if idvar exists in data.
expand	(default TRUE): if 'time' values are inconsistent, fill in missing 'time's with NAs.
safe_sep	temporary safe? separator
reverse	(default FALSE) if TRUE, the 'time' value precedes the variable name
...	additional parameters are passed to reshape.

Details

tolong is intended for the simple case in which 'wide' variables in the input data frame are identified by the fact that they contain a separator character that separates the name of the variable in the long file from the value of the 'time' variable that identifies the corresponding row in the long file, e.g x_1, x_2, x_3 or brain.volume_left, brain.volume_right. If the separator ('_' by default) occurs in other variables, it must be temporarily substituted.

reshape does not work if long variable names and time values are not fully crossed, e.g x_1, x_2, x_3, y_1, y_2. By default long creates additional variables with "NAs" so the set of variables given to reshape is fully crossed, e.g. adding a variable y_3 <- NA.

Compare the functionality of tolong with that of tidyr::gather and of tidyr::pivot_longer. 'tolong' depends on the format of variable names to identify variables whose values become new variables in the long form of the data and which labels are used as the indices of the indexing variable, whose default name is 'time', which can be set to another value with the "timevar" argument. "tolong" can handle many 'time-varying' variables. "gather" can only handle one. "pivot_longer" can handle many and might be considered a replacement for "to_long" which has the disadvantage of frequently requiring the renaming of variables, an easier task for those who have mastered the use of regular expressions, but potentially challenging otherwise.

Value

'long' file with each wide row repeated as many times as there are distinct values for the 'timevar' variable.

See Also

towide for many examples using both 'towide' and 'tolong'.

Examples

z <- data.frame(id =letters[1:10], id2= 11:20, v_L = 1:10, v_R = 11:20)
tolong(z)
tolong(z, timevar = 'Side', idvar = 'idn', ids = LETTERS[1:10])
tolong(z, timevar = 'Side', idvar = 'idn', ids = z$id2)

# unbalanced times
z <- data.frame(id =letters[1:10], id2= 11:20, v_L = 1:10, v_R = 11:20, z_L = 21:30)
tolong(z)

# a separator with multiple occurrences:
z <- data.frame(id =letters[1:10], id2= 11:20, v_a_L = 1:10, v_a_R = 11:20, z_L = 21:30)
# tolong(z) would produce an error due to multiple occurrences of the default separator '_'
names(z) <- sublast('_', '__', names(z))
tolong(z, sep = '__')

# multi-character sep
z <- data.frame(id =letters[1:10], id2= 11:20, HPC_head_R = 1:10, HPC_tail_R = 11:20, HPC_head_L = 21:30, HPC_tail_L = 31:40)
names(z) <- sub("(_[LR]$)","_\\1", names(z))
names(z)
(zz <- tolong(z, sep = "__", timevar = "Side"))
zz$id3 <- rownames(zz)
tolong(zz, idvar = 'id3' ,timevar = 'Part')

dd <- data.frame( y.a = 1:3, y.b = 1:3, x.a= 1:3, time = 1:3,
    x.b = 11:13, x.c = 21:23, id = c('a','a','b'))
tolong(dd, sep = '.')
dl <- tolong(dd, sep = '.', timevar = "type", idvar = 'patient')
towide(dl, idvar = 'patient', timevar = 'type')

# Long file with additional constants

dl <- data.frame(name = rep(c('A','B','C'), c(3,3,2)),
                 site = c('head','neck','jaw','chest')[
                   c(1,2,3,1,2,3,1,4)],
                 sex = rep(c('male','female','male'), c(3,3,2)),
                 var1 = 1:8,
                 var2 = 11:18,
                 invar = rep(1:3, c(3,3,2)))
towide(dl, c('name'), 'site')
#
# Two indexing variable: e.g. hippocampal volume 2 sides x 3 sites
#
dl <- data.frame(name = rep(LETTERS[1:3], each = 6),
                 side = rep(c('left','right'), 9),
                 site = rep(rep(c('head','body','tail'),each = 2),3),
                 volume = 1:18,
                 sex = rep(c('female','male','female'), each = 6),
                 age = rep(c(25, 43, 69), each = 6))
dl
(dlsite <- towide(dl, c('name','side'), 'site'))
(dlsite.side <- towide(dlsite, c('name'), 'side'))
#
# Flipping a data frame
#
z <- data.frame(vname = 
   rep(c('v1','v2','v3'), each = 4),
   country = rep(c('Angola','Benin','Chad','Denmark'), 3),
   code = rep(c('ANG','BEN','CHA','DEN'),3),
   val__2011 = 2011 + seq(.01,.12,.01),
   val__2012 = 2012 + seq(.01,.12,.01),
   val__2013 = 2013 + seq(.01,.12,.01),
   val__2014 = 2014 + seq(.01,.12,.01),
   val__2015 = 2015 + seq(.01,.12,.01)
)
z
z %>% 
  tolong(sep= '__') 

z %>% 
  tolong(sep= '__', timevar = 'year') %>% 
  .[!grepl('^id$',names(.))] %>% 
  towide(timevar = 'vname', idvar = c('code','year'))

## Not run: 
# Extracting chains from a stanfit object in the 'rstan' package
# If 'mod' is a stanfit model
library(rstan)
library(spida2)
df <- as.data.frame(extract(mod, permute = F))
dl <- tolong(df, sep = ':', reverse = T)

## End(Not run)

gmonette/spida2 documentation built on Aug. 20, 2023, 7:21 p.m.