R, 121 106 90 bytes

function(s,a=strsplit)cat(rep(el(a(gsub("\\d","",s),"")),pmax(el(a(s,"\\D")),"1")),sep="") 

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Saved 15 bytes by realising that rep() will coerce to numeric. Saved another 16 thanks to Giuseppe, mainly from the use of pmax to replace empty strings with 1

function(s) { x <- el(strsplit(s,"\\D")) # Split the string on anything that is not a digit... x <- pmax(x, "1")  # ... and replace any empty strings with 1. This gets us the numbers of repeats y <- gsub("\\d","",s)  # Remove all digits from the original string... y <- el(strsplit(y))  # ... and split into individual units. This gets us the symbols to repeat z <- rep(y, x)  # Carry out the required numbers of repeats. x is coerced to numeric cat(z, sep = "")  # Print without separators } 

R, 121 106 90 bytes

function(s,a=strsplit)cat(rep(el(a(gsub("\\d","",s),"")),pmax(el(a(s,"\\D")),"1")),sep="") 

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Saved 15 bytes by realising that rep() will coerce to numeric. Saved another 16 thanks to Giuseppe, mainly from the use of pmax to replace empty strings with 1

function(s) { x <- el(strsplit(s,"\\D")) # Split the string on anything that is not a digit... x <- pmax(x, "1") # ... and replace any empty strings with 1. This gets us the numbers of repeats y <- gsub("\\d","",s) # Remove all digits from the original string... y <- el(strsplit(y)) # ... and split into individual units. This gets us the symbols to repeat z <- rep(y, x) # Implement the repeats. x is coerced to numeric cat(z, sep = "") # Print without separators } 

R, 121 106 bytes

function(s,a=strsplit,x=el(a(s,"[^\\d]",,T)))cat(rep(el(a(gsub("\\d","",s),"")),ifelse(x=="",1,x)),sep="") 

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Saved 15 bytes by realising that rep() will coerce to numeric

function(s) { x <- el(strsplit(s,"[^\\d]")) # Split the string on anything that is not a digit... x <- ifelse(x=="", 1, x) # ... and replace any empty strings with 1. This gets us the numbers of repeats y <- gsub("\\d","",s) # Remove all digits from the original string... y <- el(strsplit(y)) # ... and split into individual units. This gets us the symbols to repeat z <- rep(y, x) # Carry out the required numbers of repeats. x is coerced to numeric cat(z, sep = "") # Print without separators } 

R, 121 106 90 bytes

function(s,a=strsplit)cat(rep(el(a(gsub("\\d","",s),"")),pmax(el(a(s,"\\D")),"1")),sep="") 

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Saved 15 bytes by realising that rep() will coerce to numeric. Saved another 16 thanks to Giuseppe, mainly from the use of pmax to replace empty strings with 1

function(s) { x <- el(strsplit(s,"\\D")) # Split the string on anything that is not a digit... x <- pmax(x, "1")  # ... and replace any empty strings with 1. This gets us the numbers of repeats y <- gsub("\\d","",s) # Remove all digits from the original string... y <- el(strsplit(y)) # ... and split into individual units. This gets us the symbols to repeat z <- rep(y, x) # Carry out the required numbers of repeats. x is coerced to numeric cat(z, sep = "") # Print without separators } 

R, 121 bytes

function(s,a=strsplit,x=as.numeric(el(a(s,"[^\\d]",,T))))cat(rep(el(a(gsub("\\d","",s),"")),ifelse(is.na(x),1,x)),sep="") 

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function(s) { x <- strsplit(s,"[^\\d]")  # Split the string on anything that is not a digit... x <- as.numeric(el(x)) # ...convert to numeric... x <- ifelse(is.na(x), 1, x) # ... and replace NA with 1. This gets us the numbers of repeats y <- gsub("\\d","",s) # Remove all digits from the original string... y <- el(strsplit(y)) # ... and split into individual units. This gets us the symbols to repeat z <- rep(y, x) # Carry out the required numbers of repeats cat(z, sep = "") # Print without separators } 

R, 121 106 bytes

function(s,a=strsplit,x=el(a(s,"[^\\d]",,T)))cat(rep(el(a(gsub("\\d","",s),"")),ifelse(x=="",1,x)),sep="") 

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Saved 15 bytes by realising that rep() will coerce to numeric

function(s) { x <- el(strsplit(s,"[^\\d]")) # Split the string on anything that is not a digit... x <- ifelse(x=="", 1, x)  # ... and replace any empty strings with 1. This gets us the numbers of repeats y <- gsub("\\d","",s) # Remove all digits from the original string... y <- el(strsplit(y)) # ... and split into individual units. This gets us the symbols to repeat z <- rep(y, x) # Carry out the required numbers of repeats. x is coerced to numeric cat(z, sep = "") # Print without separators }