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| 1 | +#' Baseline correction |
| 2 | +#' |
| 3 | +#' Used to remove the mean of a specified time period from the data. Currently |
| 4 | +#' only performs subtractive baseline. With a data frame, searches for |
| 5 | +#' "electrode" and "epoch" columns, and groups on these when found. An electrode |
| 6 | +#' column is always required; an epoch column is not. |
| 7 | +#' |
| 8 | +#' @author Matt Craddock \email{matt@@mattcraddock.com} |
| 9 | +#' @param data Data to be baseline corrected. |
| 10 | +#' @param ... other parameters to be passed to functions |
| 11 | +#' @export |
| 12 | + |
| 13 | +rm_baseline <- function(data, ...) { |
| 14 | + UseMethod("rm_baseline", data) |
| 15 | +} |
| 16 | + |
| 17 | +#' @param time_lim Numeric character vector (e.g. time_lim <- c(-.1, 0)). If |
| 18 | +#' none given, defaults to mean of the whole of each epoch if the data is epoched, or the |
| 19 | +#' channel mean if the data is continuous. |
| 20 | +#' @describeIn rm_baseline remove baseline from continuous \code{eeg_data} |
| 21 | +#' @export |
| 22 | + |
| 23 | +rm_baseline.eeg_data <- function(data, time_lim = NULL, ...) { |
| 24 | + |
| 25 | + if (is.null(time_lim)) { |
| 26 | + baseline_dat <- colMeans(data$signals) |
| 27 | + } else { |
| 28 | + base_times <- select_times(data, |
| 29 | + time_lim = time_lim) |
| 30 | + baseline_dat <- colMeans(base_times$signals) |
| 31 | + } |
| 32 | + data$signals <- sweep(data$signals, |
| 33 | + 2, |
| 34 | + baseline_dat, |
| 35 | + '-') |
| 36 | + data |
| 37 | +} |
| 38 | + |
| 39 | +#' @describeIn rm_baseline Remove baseline from eeg_epochs |
| 40 | +#' @export |
| 41 | + |
| 42 | +rm_baseline.eeg_epochs <- function(data, |
| 43 | + time_lim = NULL, |
| 44 | + ...) { |
| 45 | + |
| 46 | + n_epochs <- length(unique(data$timings$epoch)) |
| 47 | + n_times <- length(unique(data$timings$time)) |
| 48 | + n_chans <- ncol(data$signals) |
| 49 | + elecs <- names(data$signals) |
| 50 | + |
| 51 | + if (is.null(time_lim)) { |
| 52 | + # reshape to 3D matrix |
| 53 | + data$signals <- as.matrix(data$signals) |
| 54 | + dim(data$signals) <- c(n_times, n_epochs, n_chans) |
| 55 | + # colMeans gives an n_epochs * n_channels matrix - i.e. baseline value for |
| 56 | + # each epoch and channel |
| 57 | + baseline_dat <- colMeans(data$signals) |
| 58 | + # now we go through each timepoint subtracting the baseline values |
| 59 | + data$signals <- sweep(data$signals, |
| 60 | + c(2, 3), |
| 61 | + baseline_dat) |
| 62 | + } else { |
| 63 | + base_times <- select_times(data, |
| 64 | + time_lim = time_lim) |
| 65 | + base_times$signals <- as.matrix(base_times$signals) |
| 66 | + n_bl_times <- length(unique(base_times$timings$time)) |
| 67 | + dim(base_times$signals) <- c(n_bl_times, n_epochs, n_chans) |
| 68 | + base_times <- colMeans(base_times$signals) |
| 69 | + |
| 70 | + data$signals <- as.matrix(data$signals) |
| 71 | + dim(data$signals) <- c(n_times, n_epochs, n_chans) |
| 72 | + data$signals <- sweep(data$signals, |
| 73 | + c(2, 3), |
| 74 | + base_times, |
| 75 | + "-") |
| 76 | + } |
| 77 | + # Reshape and turn back into data frame |
| 78 | + data$signals <- array(data$signals, |
| 79 | + dim = c(n_epochs * n_times, n_chans)) |
| 80 | + data$signals <- as.data.frame(data$signals) |
| 81 | + names(data$signals) <- elecs |
| 82 | + data |
| 83 | +} |
| 84 | + |
| 85 | +#' @describeIn rm_baseline Legacy method for data.frames |
| 86 | +#' @export |
| 87 | +rm_baseline.data.frame <- function(data, |
| 88 | + time_lim = NULL, |
| 89 | + ...) { |
| 90 | + |
| 91 | + if (!("time" %in% colnames(data))) { |
| 92 | + stop("Time dimension is required.") |
| 93 | + } |
| 94 | + |
| 95 | + if (length(time_lim) == 1) { |
| 96 | + stop("time_lim should specify the full time range.") |
| 97 | + } |
| 98 | + |
| 99 | + # if the data is epoched, group by electrode and epoch; otherwise, just by |
| 100 | + # electrode. |
| 101 | + |
| 102 | + if ("epoch" %in% colnames(data)) { |
| 103 | + data <- dplyr::group_by(data, |
| 104 | + electrode, |
| 105 | + epoch, |
| 106 | + add = TRUE) |
| 107 | + } else{ |
| 108 | + data <- dplyr::group_by(data, |
| 109 | + electrode, |
| 110 | + add = TRUE) |
| 111 | + } |
| 112 | + |
| 113 | + if (is.null(time_lim)) { |
| 114 | + # if no time_lim provided, just delete mean of all time points |
| 115 | + data <- dplyr::mutate(data, |
| 116 | + amplitude = amplitude - mean(amplitude)) |
| 117 | + } else { |
| 118 | + |
| 119 | + data_sel <- dplyr::filter(data, |
| 120 | + time >= time_lim[1], |
| 121 | + time <= time_lim[2]) |
| 122 | + baseline <- dplyr::summarise(data_sel, |
| 123 | + bl = mean(amplitude)) |
| 124 | + # This is relatively memory intensive - not so bad now but would prefer |
| 125 | + # another way. Could get extremely painful with time-frequency data. |
| 126 | + data <- dplyr::left_join(data, |
| 127 | + baseline) |
| 128 | + data <- dplyr::mutate(data, |
| 129 | + amplitude = amplitude - bl) |
| 130 | + data <- dplyr::select(data, |
| 131 | + -bl) |
| 132 | + } |
| 133 | + data <- ungroup(data) |
| 134 | + data |
| 135 | +} |
| 136 | + |
| 137 | +#' @param type Type of baseline correction to apply. Options are ("divide", |
| 138 | +#' "ratio", "absolute", "db") |
| 139 | +#' @describeIn rm_baseline Method for \code{eeg_tfr} objects |
| 140 | +#' @export |
| 141 | +rm_baseline.eeg_tfr <- function(data, |
| 142 | + time_lim = NULL, |
| 143 | + type = "divide", |
| 144 | + ...) { |
| 145 | + |
| 146 | + valid_types <- c("absolute", |
| 147 | + "divide", |
| 148 | + "pc", |
| 149 | + "ratio", |
| 150 | + "db") |
| 151 | + |
| 152 | + if (!(type %in% valid_types)) { |
| 153 | + stop("Unknown baseline type ", type) |
| 154 | + } |
| 155 | + |
| 156 | + bline <- select_times(data, time_lim) |
| 157 | + bline <- colMeans(bline$signals, na.rm = TRUE) |
| 158 | + |
| 159 | + # This function implements the various baseline correction types |
| 160 | + do_corrs <- function(data, |
| 161 | + type, |
| 162 | + bline) { |
| 163 | + switch(type, |
| 164 | + "divide" = ((data - bline) / bline) * 100, |
| 165 | + "pc" = ((data - bline) / bline) * 100 - 100, |
| 166 | + "absolute" = data - bline, |
| 167 | + "db" = 10 * log10(data / bline), |
| 168 | + "ratio" = data / bline |
| 169 | + ) |
| 170 | + } |
| 171 | + |
| 172 | + orig_dims <- dim(data$signals) |
| 173 | + |
| 174 | + orig_dimnames <- dimnames(data$signals) |
| 175 | + |
| 176 | + data$signals <- apply(data$signals, |
| 177 | + 1, |
| 178 | + do_corrs, |
| 179 | + type = type, |
| 180 | + bline = bline) |
| 181 | + |
| 182 | + dim(data$signals) <- c(orig_dims[2], |
| 183 | + orig_dims[3], |
| 184 | + orig_dims[1]) |
| 185 | + |
| 186 | + data$signals <- aperm(data$signals, |
| 187 | + c(3, 1, 2)) |
| 188 | + |
| 189 | + dimnames(data$signals) <- orig_dimnames |
| 190 | + data$freq_info$baseline <- type |
| 191 | + data$freq_info$baseline_time <- time_lim |
| 192 | + data |
| 193 | +} |
| 194 | + |
| 195 | +#' @describeIn rm_baseline Method for \code{eeg_evoked} objects |
| 196 | +#' @export |
| 197 | +rm_baseline.eeg_evoked <- function(data, |
| 198 | + time_lim = NULL, |
| 199 | + ...) { |
| 200 | + |
| 201 | + if (is.null(time_lim)) { |
| 202 | + baseline_dat <- colMeans(data$signals) |
| 203 | + } else { |
| 204 | + base_times <- select_times(data, |
| 205 | + time_lim = time_lim) |
| 206 | + |
| 207 | + baseline_dat <- colMeans(base_times$signals) |
| 208 | + } |
| 209 | + data$signals <- sweep(data$signals, |
| 210 | + 2, |
| 211 | + baseline_dat, |
| 212 | + "-") |
| 213 | + data |
| 214 | +} |
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