StrippingCharacter

df <- read.csv("test.csv")
print(df)

##   col_id  pc
## 1      1 76%
## 2      2 28%
## 3      4 44%
## 4      5 42%
## 5      6 79%

str(df)

## 'data.frame':    5 obs. of  2 variables:
##  $ col_id: int  1 2 4 5 6
##  $ pc    : Factor w/ 5 levels "28%","42%","44%",..: 4 1 3 2 5

# Try stripping out that character as 'comment' i.e. not data
df <- read.csv("test.csv", comment.char = "%")
print(df)

##   col_id pc
## 1      1 76
## 2      2 28
## 3      4 44
## 4      5 42
## 5      6 79

str(df)

## 'data.frame':    5 obs. of  2 variables:
##  $ col_id: int  1 2 4 5 6
##  $ pc    : int  76 28 44 42 79