Cannot change the variable type

I can't understand why the type of the variable condition does not change with this code

df$condition <- as.character(df)
df["condition"][df["condition"] == "1"] <- "passive"
df["condition"][df["condition"] == "2"] <- "active"

I get this error message

! Assigned data `as.character(df)` must be compatible with existing data.
x Existing data has 76 rows.
x Assigned data has 3 rows.
i Only vectors of size 1 are recycled.
Backtrace:
1. base::`$<-`(`*tmp*`, condition, value = `<chr>`)
12. tibble (local) `<fn>`(`<vctrs___>`)

My data

structure(list(condition = c(2, 2, 1, 2, 2, 1, 1, 2, 2, 2, 1, 
2, 2, 1, 2, 1, 2, 1, 1, 2, 2, 2, 2, 1, 1, 1, 2, 2, 1, 1, 2, 1, 
2, 1, 1, 2, 1, 1, 2, 2, 1, 2, 1, 1, 1, 2, 2, 1, 2, 1, 1, 2, 2, 
1, 2, 1, 2, 2, 1, 1, 1, 2, 2, 1, 1, 2, 2, 2, 1, 1, 1, 1, 2, 1, 
2, 1), before= c(13, 7, 18, 18, 15, 5, 14, 5, 3, 6, 
18, 7, 5, 11, 6, 3, NA, 3, 11, 8, 10, 3, 7, 7, 12, 3, 5, 8, 4, 
9, 15, 9, 3, 16, 3, 3, 11, 3, 11, 8, 14, 21, 21, 17, 9, 3, 18, 
15, 6, 6, 12, 9, 15, 5, 13, 7, 6, 7, 9, 11, 21, 12, 7, 12, 6, 
21, 15, 21, 16, 12, 7, 18, 12, 20, 3, 10), after= c(15, 
3, 6, 18, 14, 15, 6, NA, 6, 3, 18, NA, 3, 15, NA, 15, 11, NA, 
10, 9, NA, 6, 6, 12, 3, NA, NA, 11, 9, 15, 21, 21, 6, 15, 9, 
16, 9, 11, 14, 13, 5, NA, 3, 10, NA, 3, 18, 12, NA, NA, 8, 11, 
14, NA, 13, NA, NA, 10, 6, 5, 15, 11, 12, NA, 5, NA, 15, 21, 
11, NA, 3, NA, 12, NA, 17, 15)), class = c("rowwise_df", "tbl_df", 
"tbl", "data.frame"), row.names = c(NA, -76L), groups = structure(list(
.rows = structure(list(1L, 2L, 3L, 4L, 5L, 6L, 7L, 8L, 9L, 
10L, 11L, 12L, 13L, 14L, 15L, 16L, 17L, 18L, 19L, 20L, 
21L, 22L, 23L, 24L, 25L, 26L, 27L, 28L, 29L, 30L, 31L, 
32L, 33L, 34L, 35L, 36L, 37L, 38L, 39L, 40L, 41L, 42L, 
43L, 44L, 45L, 46L, 47L, 48L, 49L, 50L, 51L, 52L, 53L, 
54L, 55L, 56L, 57L, 58L, 59L, 60L, 61L, 62L, 63L, 64L, 
65L, 66L, 67L, 68L, 69L, 70L, 71L, 72L, 73L, 74L, 75L, 
76L), ptype = integer(0), class = c("vctrs_list_of", 
"vctrs_vctr", "list"))), row.names = c(NA, -76L), class = c("tbl_df", 
"tbl", "data.frame")))

Since condition is conveniently 1 or 2, you can do:

df$condition <- c('active', 'passive')[df$condition]
# # A tibble: 76 × 3
# # Rowwise: 
#    condition before after
#    <chr>      <dbl> <dbl>
#  1 passive       13    15
#  2 passive        7     3
#  3 active        18     6
#  4 passive       18    18
#  5 passive       15    14
#  6 active         5    15
#  7 active        14     6
#  8 passive        5    NA
#  9 passive        3     6
# 10 passive        6     3
# # … with 66 more rows
# # ℹ Use `print(n = ...)` to see more rows

I suggest not to change your numeric to characters, but directly make a factor of it like this

df$condition <- factor(df$condition, levels = c(1, 2), labels = c("passive", "active"))

Or using tidyverse / dyplr

df %>%
mutate(condition = factor(condition, c(1, 2), c("passive", "active")))
# A tibble: 76 × 3
# Rowwise: 
condition before after
<fct>      <dbl> <dbl>
1 active        13    15
2 active         7     3
3 passive       18     6
4 active        18    18
5 active        15    14
6 passive        5    15
7 passive       14     6
8 active         5    NA
9 active         3     6
10 active         6     3
# … with 66 more rows
# ℹ Use `print(n = ...)` to see more rows