Error with subscript within list of axis labels-CodePudding

I have a list of axis labels for various water properties. Some have chemical formulae that need subscript. However, I keep getting an error of: non-numeric argument to binary operator.

This is the code for the subscript.

axisLabels <- list('DA' = c('Dissolved Ammonium (NH'[4]*') \n(mg/l)', 'Sampling Site'),
               'DNI' = c('Dissolved Nitrite \n(mg NO'[2]*'/L)', 'Sampling Site'),
               'DNA' = c('Dissolved Nitrate \n(NO'[3]*')', 'Sampling Site'),
               'DS' = c('Dissolved Sulphate \n(mg SO'[4]*'/L)', 'Sampling Site'))

This is the Error:

Error in "Dissolved Ammonium (NH"[4] * ") \n(mg/l)" : 
non-numeric argument to binary operator

CodePudding user response：

Your syntax is wrong here. If you want to use square brackets to indicate subscripts, that can only be done in the context of plotmath expressions:

axisLabels <- list('DA' = expression(Dissolved~Ammonium~(NH[4])~mg/l),
                   'DNI' = expression(Dissolved~Nitrite~(mg~NO[2]/L)),
                   'DNA' = expression(Dissolved~Nitrate~(NO[3])),
                   'DS' = expression(Dissolved~Sulphate~(mg~SO[4]/L)))

par(mfrow = c(2, 2))
lapply(axisLabels, function(x) plot(1:10, rnorm(10), xlab = x))

Or, if you want line breaks, you can use unicode escapes to get your subscript numbers:

axisLabels <- list('DA' = c('Dissolved Ammonium (NH\u2084) \n(mg/l)'),
               'DNI' = c('Dissolved Nitrite \n(mg NO\u2082/L)'),
               'DNA' = c('Dissolved Nitrate \n(NO\u2083)'),
               'DS' = c('Dissolved Sulphate \n(mg SO\u2084/L)'))

par(mfrow = c(2, 2))
lapply(axisLabels, function(x) plot(1:10, rnorm(10), xlab = x))