Shift Array by Index

Re-arrange arrays in parallel

Usage

shift_array(x, shift_idx, shift_by, shift_amount)

Arguments

x

array, must have at least matrix

shift_idx

which index is to be shifted

shift_by

which dimension decides shift_amount

shift_amount

shift amount along shift_idx

Details

A simple use-case for this function is to think of a matrix where each row is a signal and columns stand for time. The objective is to align (time-lock) each signal according to certain events. For each signal, we want to shift the time points by certain amount.

In this case, the shift amount is defined by shift_amount, whose length equals to number of signals. shift_idx=2 as we want to shift time points (column, the second dimension) for each signal. shift_by=1 because the shift amount is depend on the signal number.

Examples

x <- matrix(1:10, nrow = 2, byrow = TRUE)
z <- shift_array(x, 2, 1, c(1,2))

y <- NA * x
y[1,1:4] = x[1,2:5]
y[2,1:3] = x[2,3:5]

# Check if z ang y are the same
z - y
#>      [,1] [,2] [,3] [,4] [,5]
#> [1,]    0    0    0    0   NA
#> [2,]    0    0    0   NA   NA

# array case
# x is Trial x Frequency x Time
x <- array(1:27, c(3,3,3))

# Shift time for each trial, amount is 1, -1, 0
shift_amount <- c(1,-1,0)
z <- shift_array(x, 3, 1, shift_amount)

if(interactive()){

par(mfrow = c(3, 2))
for( ii in 1:3 ){
  image(t(x[ii, ,]), ylab = 'Frequency', xlab = 'Time',
        main = paste('Trial', ii))
  image(t(z[ii, ,]), ylab = 'Frequency', xlab = 'Time',
        main = paste('Shifted amount:', shift_amount[ii]))
}

}