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#' siunitx.uncertainty
#'
#' Writing number with exponent (such as scientific notation) with uncertainty using siunitx
#'
#' @param quantity quantity
#' @param uncertainty uncertainty
#' @param digits number of digits
#'
#' @return a string suitable for use with siunitx num{} command
#' @export
siunitx.uncertainty <- function(quantity, uncertainty, digits = 6) {
# Origin of problem, this kind of code:
# \SI[separate-uncertainty=true]{\Sexpr{formatC(cd.flux, format = "e", digits = 2)} \pm \Sexpr{formatC(cd.flux.error, format = "e", digits = 2)}}{\milli\coulomb\per\square\cm\per\second}
# makes siunitx throw the error:
# !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
# !
# ! siunitx error: "misplaced-sign-token"
# !
# ! Misplaced sign token '\pm '.
# !
# ! See the siunitx documentation for further information.
# !
# ! For immediate help type H <return>.
# !...............................................
# This is status-by-design according to Joseph Wright.
# http://tex.stackexchange.com/questions/123771/exponent-notation-in-siunitx
# But if the two numbers (number and uncertainty) have the same exponent, that is ok.
# So here we try to write a function that accepts two numbers,
# and returns them written in a common exponent (as strings).
# both arguments should be numeric
# how to find common exponent for two numbers?
# find exponent of quantity (tiopotensen for kvantiteten)
quantity.exponent <- floor(log(abs(quantity), 10))
# find coefficient of quantity
# warning, numeric-to-string-to-numeric conversion ...
quantity.coefficient <-
as.numeric(strsplit(formatC(quantity, format="e", digits=digits), "[Ee]-")[[1]][1])
# construct return quantity string
rquantity.string <-
paste0(formatC(quantity.coefficient, format="f", digits=digits), "e", quantity.exponent)
# find exponent of uncertainty (tiopotensen for the uncertainty)
uncertainty.exponent <- floor(log(abs(uncertainty), 10))
# find coefficient of uncertainty
# warning, numeric-to-string-to-numeric conversion ...
uncertainty.coefficient <-
as.numeric(strsplit(formatC(uncertainty, format="e", digits=digits), "[Ee]-")[[1]][1])
# adjust uncertainty to the same exponent as the quantity
# express uncertainty with the same exponent as quantity
# (adjust number of uncertainty accordingly)
runcertainty.exponent <- quantity.exponent
runcertainty.coefficient <- uncertainty.coefficient * 10^(uncertainty.exponent - quantity.exponent)
runcertainty.string <-
paste0(formatC(runcertainty.coefficient, format="f", digits=digits), "e", runcertainty.exponent)
# create a string directly suitable for the siunitx \num{} command
siunitx.string <- paste(quantity.coefficient, "\\pm", runcertainty.string)
return(c(quantity = rquantity.string,
uncertainty = runcertainty.string,
siunitx = siunitx.string))
}