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R

# AUTOLAB.R
# Functions to read and manipulate data from AUTOLAB potentiostats/galvanostats
# Taha Ahmed, June 2011
# CONTENTS
source("/home/taha/chepec/chetex/common/R/common.R")
# >>>> chronoamp2df
##################################################
################# chronoamp2df ###################
##################################################
chronoamp2df <- function(datafilename, wearea = 1) {
## Description:
## Reads current-time data (from AUTOLAB potentiostat)
## and returns a dataframe with the data and some
## calculated quantities based on the data.
## Usage:
## chronoamp2df(datafilename, wearea)
## Arguments:
## datafilename: text string with full path to experimental file
## wearea: (optional) area of working electrode (in square centimeters)
## Value:
## Dataframe with the following columns:
## $ sampleid : chr
## $ time : num
## $ current : num
## $ currentdensity : num
## $ timediff : num
## $ dIdt : num
## $ didt : num
## $ charge : num
## $ chargedensity : num
#
datafile <- file(datafilename, "r")
chifile <- readLines(datafile, n = -1) #read all lines of input file
close(datafile)
#
sampleid <- ProvideSampleId(datafilename)
#
rgxp.number <- "^\\d+\\.\\d+"
# regexp that matches a decimal number at the beginning of the line.
# Matches numbers _without_ a negative sign (hyphen),
# followed by one or more digits before the decimal, a decimal point,
# and an one or more digits after the decimal point.
# Note that backslashes are escaped.
#
numrow.idx <- regexpr(rgxp.number, chifile)
# Save the match length attribute to another variable,
numrow.len <- attr(numrow.idx, "match.length")
# then scrap the attribute of the original variable.
attr(numrow.idx, "match.length") <- NULL
#
i <- seq(1, length(numrow.idx) - 1, 1)
j <- seq(2, length(numrow.idx), 1)
# Start indices of data ranges
starts <- which(numrow.idx[i] != 1 & numrow.idx[j] == 1) + 1
# End indices, except for the last
ends <- which(numrow.idx[i] == 1 & numrow.idx[j] != 1)
# Fix the last index of end indices
ends <- c(ends, length(numrow.idx))
#
ff <- data.frame(NULL)
for (s in 1:length(starts)) {
zz <- textConnection(chifile[starts[s]:ends[s]], "r")
ff <- rbind(ff,
data.frame(sampleid,
matrix(scan(zz, what = numeric(), sep = ""),
ncol = 2, byrow = T)))
close(zz)
}
names(ff) <- c("sampleid", "time", "current")
# Calculate current density
currentdensity <- ff$current / wearea
ff <- cbind(ff, currentdensity = currentdensity)
# Calculate time diff and current diff
timediff <- c(ff$time[1], diff(ff$time))
currentdiff <- c(ff$current[1], diff(ff$current))
currentdensitydiff <- c(ff$currentdensity[1], diff(ff$currentdensity))
# Calculate differential of current and current density
dIdt <- currentdiff / timediff
didt <- currentdensitydiff / timediff
# Calculate charge and charge density
charge <- cumsum(ff$current)
chargedensity <- cumsum(ff$currentdensity)
# Update ff dataframe
ff <- cbind(ff,
timediff = timediff,
dIdt = dIdt,
didt = didt,
charge = charge,
chargedensity = chargedensity)
#
return(ff)
}