chi squared - Why 2 outputs of chisq.test are different in R -

in following, why outputs of 2 chisq.test different, when data same:

> df1   count position 1     1       11 2     6       12 3    12       13 4    23       14 5    27       15 > df2   count position 1     1       11 2     4       12 3     9       13 4    24       14 5    24       15 > mm = merge(df1, df2,  by='position') > mm   position count.x count.y 1       11       1       1 2       12       6       4 3       13      12       9 4       14      23      24 5       15      27      24 

first method:

> chisq.test(mm[2:3])          pearson's chi-squared test  data:  mm[2:3] x-squared = 0.6541, df = 4, p-value = 0.9569  warning message: in chisq.test(mm[2:3]) : chi-squared approximation may incorrect 

second method:

> chisq.test(df1$count, df2$count)          pearson's chi-squared test  data:  df1$count , df2$count x-squared = 15, df = 12, p-value = 0.2414  warning message: in chisq.test(df1$count, df2$count) :   chi-squared approximation may incorrect >  

edit: responding comment: following identical:

> mm[2:3]   count.x count.y 1       1       1 2       6       4 3      12       9 4      23      24 5      27      24 >   > mm[,2:3]   count.x count.y 1       1       1 2       6       4 3      12       9 4      23      24 5      27      24 

data:

> dput(df1) structure(list(count = c(1l, 6l, 12l, 23l, 27l), position = 11:15), .names = c("count",  "position"), class = "data.frame", row.names = c(na, -5l)) > dput(df2) structure(list(count = c(1l, 4l, 9l, 24l, 24l), position = 11:15), .names = c("count",  "position"), class = "data.frame", row.names = c(na, -5l)) 

see ?chisq : in first case, mm[2:3] taken contingency table, in second case, contingency table computed.

chisq.test(table(df1$count, df2$count))          pearson's chi-squared test  data:  table(df1$count, df2$count) x-squared = 15, df = 12, p-value = 0.2414  warning message: in chisq.test(table(df1$count, df2$count)) :   chi-squared approximation may incorrect 

so, really, calculated chisq of table :

     1 4 9 24   1  1 0 0  0   6  0 1 0  0   12 0 0 1  0   23 0 0 0  1   27 0 0 0  1